diff --git a/html/semantics/popovers/popover-animated-display-ref.html b/html/semantics/popovers/popover-animated-display-ref.html
deleted file mode 100644
index 477a97c12ccd9d..00000000000000
--- a/html/semantics/popovers/popover-animated-display-ref.html
+++ /dev/null
@@ -1,26 +0,0 @@
-<!DOCTYPE html>
-<link rel="stylesheet" href="resources/popover-styles.css">
-
-<div class=topmost></div>
-<div class=fake-popover>This is a popover</div>
-
-
-<style>
-  .fake-popover {
-    width: 100px;
-    height: 100px;
-    margin: 1em;
-    /* The animated property */
-    left: 100px;
-  }
-  .topmost {
-    position:fixed;
-    top:0;
-    left:0;
-    width:1000px;
-    height:1000px;
-    background:green;
-    margin:0;
-    padding:0;
-  }
-</style>
diff --git a/html/semantics/popovers/popover-animated-hide-cleanup.html b/html/semantics/popovers/popover-animated-hide-cleanup.html
deleted file mode 100644
index 9310acc4ff2098..00000000000000
--- a/html/semantics/popovers/popover-animated-hide-cleanup.html
+++ /dev/null
@@ -1,98 +0,0 @@
-
-<!DOCTYPE html>
-<meta charset="utf-8">
-<link rel=author href="mailto:masonf@chromium.org">
-<link rel=help href="https://open-ui.org/components/popup.research.explainer">
-<script src="/resources/testharness.js"></script>
-<script src="/resources/testharnessreport.js"></script>
-<script src="/resources/testdriver.js"></script>
-<script src="/resources/testdriver-actions.js"></script>
-<script src="/resources/testdriver-vendor.js"></script>
-<script src="resources/popover-utils.js"></script>
-<script src="/common/gc.js"></script>
-
-<dialog>I am a dialog</dialog>
-
-<style>
-[popover].animation {
-  left: 0px;
-}
-[popover].animation:open {
-  animation: move 1000s;
-}
-@keyframes move {
-  from { left: 0px; }
-  to { left: 200px; }
-}
-
-[popover].transition {
-  opacity: 0;
-  transition: opacity 5s;
-}
-[popover].transition:open {
-  opacity: 1;
-}
-
-[popover] {
-  top: 200px;
-}
-[popover]::backdrop {
-  background-color: rgba(255,0,0,0.2);
-}
-</style>
-
-<script>
-function rAF() {
-  return new Promise(resolve => requestAnimationFrame(resolve));
-}
-function addPopover(classname) {
-  const popover = document.createElement('div');
-  popover.popover = 'auto';
-  popover.classList = classname;
-  popover.textContent = 'This is a popover';
-  document.body.appendChild(popover);
-  return popover;
-}
-promise_test(async () => {
-  let popover = addPopover("animation");
-  let dialog = document.querySelector('dialog');
-  popover.showPopover(); // No animations here
-  await rAF();
-  popover.hidePopover(); // Start animations
-  await rAF();
-  popover.remove();
-  await garbageCollect();
-  await rAF();
-  // This test passes if it does not crash.
-},'Ensure no crashes if running animations are immediately cancelled (document removal)');
-
-promise_test(async (t) => {
-  let popover = addPopover("animation");
-  let dialog = document.querySelector('dialog');
-  popover.showPopover(); // No animations here
-  await rAF();
-  popover.hidePopover(); // Start animations
-  await rAF();
-  dialog.showModal(); // Immediately hide popover
-  t.add_cleanup(() => dialog.close());
-  await rAF();
-  popover.remove();
-  await garbageCollect();
-  await rAF();
-  // This test passes if it does not crash.
-},'Ensure no crashes if running animations are immediately cancelled (dialog showModal)');
-
-promise_test(async (t) => {
-  let popover = addPopover("transition");
-  let dialog = document.querySelector('dialog');
-  let button = document.createElement('button');
-  t.add_cleanup(() => {popover.remove();button.remove();});
-  document.body.appendChild(button);
-  button.addEventListener('click',() => dialog.show());
-  popover.showPopover(); // No animations here
-  await rAF();
-  await clickOn(button);
-  await rAF();
-  // This test passes if it does not crash.
-},'Ensure no crashes if running transitions are immediately cancelled (button click)');
-</script>
diff --git a/html/semantics/popovers/popover-animated-hide-display.html b/html/semantics/popovers/popover-animated-hide-display.html
deleted file mode 100644
index b914d80e69aefa..00000000000000
--- a/html/semantics/popovers/popover-animated-hide-display.html
+++ /dev/null
@@ -1,57 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait">
-<meta charset="utf-8">
-<link rel=author href="mailto:masonf@chromium.org">
-<link rel=help href="https://open-ui.org/components/popup.research.explainer">
-<link rel=match href="popover-animated-display-ref.html">
-
-<div popover>This is a popover</div>
-<div class=topmost></div>
-
-<style>
-  [popover] {
-    width: 100px;
-    height: 100px;
-    margin: 1em;
-    left: 0;
-    transition: left 20s steps(2, jump-end) -10s;
-  }
-  [popover]:open {
-    left: 200px;
-  }
-  .topmost {
-    position:fixed;
-    z-index: 999999;
-    top:0;
-    left:0;
-    width:1000px;
-    height:1000px;
-    background:green;
-    margin:0;
-    padding:0;
-  }
-</style>
-
-<script>
-window.onload = () => {
-  requestAnimationFrame(() => {
-    requestAnimationFrame(() => {
-      // This will show the popover, hide the popover, and start the transition.
-      const popover = document.querySelector('[popover]');
-      popover.showPopover();
-      popover.getAnimations()[0].finish();
-      if (getComputedStyle(popover).left != "200px")
-        popover.remove();
-      popover.hidePopover();
-      document.getAnimations()[0].ready.then(() => {
-        requestAnimationFrame(() => {
-          requestAnimationFrame(() => {
-            // Take a screenshot now.
-            document.documentElement.classList.remove('reftest-wait');
-          });
-        });
-      });
-    });
-  });
-}
-</script>
diff --git a/html/semantics/popovers/popover-animated-hide-finishes-ref.html b/html/semantics/popovers/popover-animated-hide-finishes-ref.html
deleted file mode 100644
index d8334f985ed51f..00000000000000
--- a/html/semantics/popovers/popover-animated-hide-finishes-ref.html
+++ /dev/null
@@ -1,16 +0,0 @@
-<!DOCTYPE html>
-
-<div class=topmost></div>
-
-<style>
-  .topmost {
-    position:fixed;
-    top:0;
-    left:0;
-    width:1000px;
-    height:1000px;
-    background:green;
-    margin:0;
-    padding:0;
-  }
-</style>
diff --git a/html/semantics/popovers/popover-animated-hide-finishes.html b/html/semantics/popovers/popover-animated-hide-finishes.html
deleted file mode 100644
index 1af583b5a8315d..00000000000000
--- a/html/semantics/popovers/popover-animated-hide-finishes.html
+++ /dev/null
@@ -1,56 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait">
-<meta charset="utf-8">
-<link rel=author href="mailto:masonf@chromium.org">
-<link rel=help href="https://open-ui.org/components/popup.research.explainer">
-<link rel=match href="popover-animated-hide-finishes-ref.html">
-
-<div popover>This is a popover</div>
-<div class=topmost></div>
-
-<style>
-  [popover] {
-    width: 100px;
-    height: 100px;
-    margin: 1em;
-    left: 0;
-    /* Immediate transition: */
-    transition: left 1s -1s;
-  }
-  [popover]:open {
-    left: 200px;
-  }
-  [popover]::backdrop {
-    background-color: red;
-  }
-  .topmost {
-    position:fixed;
-    z-index: 999999;
-    top:0;
-    left:0;
-    width:1000px;
-    height:1000px;
-    background:green;
-    margin:0;
-    padding:0;
-  }
-</style>
-
-<script>
-window.onload = () => {
-  requestAnimationFrame(() => {
-    requestAnimationFrame(() => {
-      // This will show the popover, hide the popover, and start the hide transition,
-      // which should immediately finish.
-      document.querySelector('[popover]').showPopover();
-      document.querySelector('[popover]').hidePopover();
-      requestAnimationFrame(() => {
-        requestAnimationFrame(() => {
-          // Take a screenshot now.
-          document.documentElement.classList.remove('reftest-wait');
-        });
-      });
-    });
-  });
-}
-</script>
diff --git a/html/semantics/popovers/popover-animated-show-display.html b/html/semantics/popovers/popover-animated-show-display.html
deleted file mode 100644
index 6857103a759b2c..00000000000000
--- a/html/semantics/popovers/popover-animated-show-display.html
+++ /dev/null
@@ -1,52 +0,0 @@
-<!DOCTYPE html>
-<html class="reftest-wait">
-<meta charset="utf-8">
-<link rel=author href="mailto:masonf@chromium.org">
-<link rel=help href="https://open-ui.org/components/popup.research.explainer">
-<link rel=match href="popover-animated-display-ref.html">
-
-<div popover>This is a popover</div>
-<div class=topmost></div>
-
-<style>
-  [popover] {
-    width: 100px;
-    height: 100px;
-    margin: 1em;
-    left: 0;
-    transition: left 20s steps(2, jump-end) -10s;
-  }
-  [popover]:open {
-    left: 200px;
-  }
-  .topmost {
-    position:fixed;
-    z-index: 999999;
-    top:0;
-    left:0;
-    width:1000px;
-    height:1000px;
-    background:green;
-    margin:0;
-    padding:0;
-  }
-</style>
-
-<script>
-window.onload = () => {
-  requestAnimationFrame(() => {
-    requestAnimationFrame(() => {
-      // This will show the popover, and start the transition.
-      document.querySelector('[popover]').showPopover();
-      document.getAnimations()[0].ready.then(() => {
-        requestAnimationFrame(() => {
-          requestAnimationFrame(() => {
-            // Take a screenshot now.
-            document.documentElement.classList.remove('reftest-wait');
-          });
-        });
-      });
-    });
-  });
-}
-</script>
diff --git a/html/semantics/popovers/popover-animation-corner-cases.html b/html/semantics/popovers/popover-animation-corner-cases.html
deleted file mode 100644
index f41f7a68df9058..00000000000000
--- a/html/semantics/popovers/popover-animation-corner-cases.html
+++ /dev/null
@@ -1,230 +0,0 @@
-
-<!DOCTYPE html>
-<meta charset="utf-8">
-<link rel=author href="mailto:masonf@chromium.org">
-<link rel=help href="https://open-ui.org/components/popup.research.explainer">
-<script src="/resources/testharness.js"></script>
-<script src="/resources/testharnessreport.js"></script>
-<script src="resources/popover-utils.js"></script>
-
-<body>
-<style>
-.animation { opacity: 0; }
-.animation:open { opacity: 1; }
-.animation:not(:open) { animation: fade-out 1000s; }
-@keyframes fade-out {
-  from { opacity: 1; }
-  to { opacity: 0; }
-}
-
-.animation>div>div { left: 0; }
-.animation:not(:open)>div>div { animation: rotate 1000s; color:red;}
-@keyframes rotate {
-  from { transform: rotate(0); }
-  to { transform: rotate(360deg); }
-}
-
-[popover] { top: 200px; }
-[popover]::backdrop { background-color: rgba(255,0,0,0.2); }
-</style>
-
-<script>
-function createPopover(t,type) {
-  const popover = document.createElement('div');
-  popover.popover = 'auto';
-  popover.classList = type;
-  const div = document.createElement('div');
-  const descendent = div.appendChild(document.createElement('div'));
-  descendent.appendChild(document.createTextNode("Descendent element"));
-  popover.append("This is a pop up",div);
-  document.body.appendChild(popover);
-  t.add_cleanup(() => popover.remove());
-  return {popover, descendent};
-}
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'animation');
-  assert_false(isElementVisible(popover));
-  assert_equals(descendent.parentElement.parentElement,popover);
-  assert_true(popover.matches(':closed'));
-  assert_false(popover.matches(':open'));
-  popover.showPopover();
-  assert_false(popover.matches(':closed'));
-  assert_true(popover.matches(':open'));
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  popover.hidePopover();
-  const animations = popover.getAnimations({subtree: true});
-  assert_equals(animations.length,2,'There should be two animations running');
-  assert_false(popover.matches(':open'),'popover should not match :open as soon as hidden');
-  assert_false(popover.matches(':closed'),'popover should not match :closed until animations complete');
-  assert_true(isElementVisible(popover),'but animations should keep the popover visible');
-  assert_true(isElementVisible(descendent),'The descendent should also be visible');
-  await waitForRender();
-  await waitForRender();
-  assert_equals(popover.getAnimations({subtree: true}).length,2,'The animations should still be running');
-  assert_true(isElementVisible(popover),'Popover should still be visible due to animation');
-  animations.forEach(animation => animation.finish()); // Force the animations to finish
-  await waitForRender(); // Wait one frame
-  assert_true(popover.matches(':closed'),'The pop up should now match :closed');
-  assert_false(popover.matches(':open'),'The pop up still shouldn\'t match :open');
-  assert_false(isElementVisible(popover),'The pop up should now be invisible');
-  assert_false(isElementVisible(descendent),'The descendent should also be invisible');
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-},'Descendent animations should keep the pop up visible until the animation ends');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  assert_equals(popover.classList.length, 0);
-  assert_false(isElementVisible(popover));
-  popover.showPopover();
-  assert_true(popover.matches(':open'));
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  // Start an animation on the popover and its descendent.
-  popover.animate([{opacity: 1},{opacity: 0}],{duration: 1000000,iterations: 1});
-  descendent.animate([{transform: 'rotate(0)'},{transform: 'rotate(360deg)'}],1000000);
-  assert_equals(popover.getAnimations({subtree: true}).length,2);
-  // Then hide the popover.
-  popover.hidePopover();
-  assert_false(popover.matches(':open'),'pop up should not match :open as soon as hidden');
-  assert_true(popover.matches(':closed'),'pop up should match :closed immediately');
-  assert_equals(popover.getAnimations({subtree: true}).length,2,'animations should still be running');
-  await waitForRender();
-  assert_equals(popover.getAnimations({subtree: true}).length,2,'animations should still be running');
-  assert_false(isElementVisible(popover),'Pre-existing animations should not keep the pop up visible');
-},'Pre-existing animations should *not* keep the pop up visible until the animation ends');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  popover.showPopover();
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  let animation;
-  popover.addEventListener('beforetoggle', (e) => {
-    if (e.newState !== "closed")
-      return;
-    animation = popover.animate([{opacity: 1},{opacity: 0}],1000000);
-  });
-  assert_equals(popover.getAnimations({subtree: true}).length,0,'There should be no animations yet');
-  popover.hidePopover();
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should now be running');
-  assert_true(!!animation);
-  assert_true(isElementVisible(popover),'The animation should keep the popover visible');
-  animation.finish();
-  await waitForRender();
-  assert_false(isElementVisible(popover),'Once the animation ends, the popover is hidden');
-},'It should be possible to use the "beforetoggle" event handler to animate the hide');
-
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  const dialog = document.body.appendChild(document.createElement('dialog'));
-  t.add_cleanup(() => dialog.remove());
-  popover.showPopover();
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  let animation;
-  popover.addEventListener('beforetoggle', (e) => {
-    if (e.newState !== "closed")
-      return;
-    animation = popover.animate([{opacity: 1},{opacity: 0}],1000000);
-  });
-  assert_equals(popover.getAnimations({subtree: true}).length,0,'There should be no animations yet');
-  dialog.showModal(); // Force hide the popover
-  await waitForRender();
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should now be running');
-  assert_true(isElementVisible(popover),'And the animation should keep the popover visible');
-  animation.finish();
-  await waitForRender();
-  assert_false(isElementVisible(popover),'Once the animation ends, the popover is hidden');
-},'It should be possible to use the "beforetoggle" event handler to animate the hide, even when the hide is due to dialog.showModal');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  popover.showPopover();
-  assert_true(isElementVisible(popover));
-  popover.addEventListener('beforetoggle', (e) => e.preventDefault());
-  popover.hidePopover();
-  await waitForRender();
-  assert_false(isElementVisible(popover),'Even if hide event is cancelled, the popover still closes');
-},'toggle event cannot be cancelled');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'animation');
-  assert_false(isElementVisible(popover));
-  popover.showPopover();
-  assert_false(popover.matches(':closed'));
-  assert_true(popover.matches(':open'));
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  popover.popover = 'manual';
-  const animations = popover.getAnimations({subtree: true});
-  assert_equals(animations.length,2,'There should be two animations running');
-  assert_false(popover.matches(':open'),'popover should not match :open as soon as hidden');
-  assert_false(popover.matches(':closed'),'popover should not match :closed until animations complete');
-  assert_true(isElementVisible(popover),'but animations should keep the popover visible');
-  animations.forEach(animation => animation.finish()); // Force the animations to finish
-  await waitForRender(); // Wait one frame
-  assert_true(popover.matches(':closed'),'The pop up should now match :closed');
-  assert_false(popover.matches(':open'),'The pop up still shouldn\'t match :open');
-  assert_false(isElementVisible(popover),'The pop up should now be invisible');
-},'Closing animations are triggered by changing the popover type');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  popover.showPopover();
-  assert_true(isElementVisible(popover));
-  assert_equals(popover.getAnimations({subtree: true}).length,0);
-  popover.addEventListener('beforetoggle', (e) => {
-    if (e.newState !== "closed")
-      return;
-    popover.animate([{opacity: 1},{opacity: 0}],1000000);
-  });
-  assert_equals(popover.getAnimations({subtree: true}).length,0,'There should be no animations yet');
-  popover.hidePopover();
-  await waitForRender();
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should now be running');
-  assert_true(isElementVisible(popover),'The popover should still be visible because the animation hasn\'t ended.');
-  const animation = popover.getAnimations({subtree: true})[0];
-
-  animation.dispatchEvent(new Event('finish'));
-  await waitForRender();
-  assert_true(isElementVisible(popover),'Synthetic finish events should not stop the animation, so the popover should still be visible.');
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should still be running');
-
-  animation.dispatchEvent(new Event('cancel'));
-  await waitForRender();
-  assert_true(isElementVisible(popover),'Synthetic cancel events should not stop the animation, so the popover should still be visible.');
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'the hide animation should still be running');
-},'animation finish/cancel events must be trusted in order to finish closing the popover.');
-
-promise_test(async (t) => {
-  const {popover, descendent} = createPopover(t,'');
-  popover.showPopover();
-  popover.addEventListener('beforetoggle', (e) => {
-    if (e.newState !== "closed")
-      return;
-    popover.animate([{opacity: 1},{opacity: 0}],1000000);
-  });
-  popover.hidePopover();
-  await waitForRender();
-  assert_true(isElementVisible(popover),'The popover should still be visible because the animation hasn\'t ended.');
-  assert_equals(popover.getAnimations({subtree: true}).length,1,'There should be one animation running');
-  const animation = popover.getAnimations({subtree: true})[0];
-  let new_animation;
-  const listener = () => {new_animation = popover.animate([{opacity: 1},{opacity: 0}],1000000)};
-  animation.addEventListener('finish',listener,{capture:true});
-  animation.addEventListener('cancel',listener,{capture:true});
-  popover.addEventListener('animationfinish',listener,{capture:true});
-  popover.addEventListener('animationcancel',listener,{capture:true});
-  assert_true(isElementVisible(popover),'The popover should still be visible.');
-  assert_equals(new_animation, undefined,'New animation should not be started yet.');
-  animation.finish();
-  await waitForRender(); // Wait one frame
-  assert_true(popover.matches(':closed'),'The pop up should now match :closed');
-  assert_false(popover.matches(':open'),'The pop up still shouldn\'t match :open');
-  assert_false(isElementVisible(popover),'The pop up should now be invisible');
-  assert_not_equals(new_animation, animation);
-  assert_equals(popover.getAnimations({subtree: true})[0],new_animation,'The new animation should now be running');
-},'Capturing event listeners can\'t affect popover animations.');
-</script>
diff --git a/html/semantics/popovers/popover-attribute-basic.html b/html/semantics/popovers/popover-attribute-basic.html
index bc32c357d3a550..0abba9c4e87f7a 100644
--- a/html/semantics/popovers/popover-attribute-basic.html
+++ b/html/semantics/popovers/popover-attribute-basic.html
@@ -32,16 +32,8 @@
   <dialog open>Dialog without popover attribute</dialog>
 </div>
 
-<div popover class=animated>Animated popover</div>
 <div id=outside></div>
 <style>
-[popover].animated {
-  opacity: 0;
-  transition: opacity 10s;
-}
-[popover].animated:open {
-  opacity: 1;
-}
 [popover] {
   inset:auto;
   top:0;
@@ -106,11 +98,11 @@
     // be invisible. Otherwise, it should be visible.
     const expectVisible = !nonPopover.hasAttribute('popover');
     assertPopoverVisibility(nonPopover, /*isPopover*/false, expectVisible, 'A non-popover should start out visible');
-    assert_throws_dom("InvalidStateError",() => nonPopover.showPopover(),'Calling showPopover on a non-popover should throw InvalidStateError');
+    assert_throws_dom("NotSupportedError",() => nonPopover.showPopover(),'Calling showPopover on a non-popover should throw NotSupported');
     assertPopoverVisibility(nonPopover, /*isPopover*/false, expectVisible, 'Calling showPopover on a non-popover should leave it visible');
-    assert_throws_dom("InvalidStateError",() => nonPopover.hidePopover(),'Calling hidePopover on a non-popover should throw InvalidStateError');
+    assert_throws_dom("NotSupportedError",() => nonPopover.hidePopover(),'Calling hidePopover on a non-popover should throw NotSupported');
     assertPopoverVisibility(nonPopover, /*isPopover*/false, expectVisible, 'Calling hidePopover on a non-popover should leave it visible');
-    assert_throws_dom("InvalidStateError",() => nonPopover.togglePopover(),'Calling togglePopover on a non-popover should throw InvalidStateError');
+    assert_throws_dom("NotSupportedError",() => nonPopover.togglePopover(),'Calling togglePopover on a non-popover should throw NotSupported');
     assertPopoverVisibility(nonPopover, /*isPopover*/false, expectVisible, 'Calling togglePopover on a non-popover should leave it visible');
   }
 
@@ -406,28 +398,6 @@
     });
   });
 
-  promise_test(async () => {
-    const popover = document.querySelector('[popover].animated');
-    assert_true(!!popover);
-    assert_false(isElementVisible(popover));
-    popover.showPopover();
-    assert_true(popover.matches(':open'));
-    assert_false(popover.matches(':closed'));
-    assert_true(getComputedStyle(popover).opacity < 0.1,'Animations should start on show');
-    assert_throws_dom("InvalidStateError",() => popover.showPopover(),'Calling showPopover on a popover that is in the process of animating show should throw InvalidStateError');
-    await finishAnimations(popover);
-    assert_true(getComputedStyle(popover).opacity > 0.9);
-    assert_true(isElementVisible(popover));
-    popover.hidePopover();
-    assert_false(popover.matches(':open'));
-    assert_false(popover.matches(':closed'),'Not :closed until animations finish');
-    assert_true(getComputedStyle(popover).opacity > 0.9,'Animations should start on hide');
-    assert_throws_dom("InvalidStateError",() => popover.hidePopover(),'Calling hidePopover on a popover that is in the process of animating hide should throw InvalidStateError');
-    assert_throws_dom("InvalidStateError",() => popover.showPopover(),'Calling showPopover on a popover that is in the process of animating hide should throw InvalidStateError');
-    await finishAnimations(popover);
-    assert_true(popover.matches(':closed'),':closed should match once animations finish');
-  },'Exceptions are thrown even when show/hide are animated');
-
   done();
 };
 </script>
diff --git a/html/semantics/popovers/popover-focus.html b/html/semantics/popovers/popover-focus.html
index b1e59a13971c7b..307ca8a80f553c 100644
--- a/html/semantics/popovers/popover-focus.html
+++ b/html/semantics/popovers/popover-focus.html
@@ -54,15 +54,6 @@
     border: 2px solid black;
     top:150px;
     left:150px;
-    opacity: 0;
-  }
-  [popover]:not(:open) {
-    /* Add a *hide* transition to all popovers, to make sure animations don't
-       affect focus management */
-    transition: opacity 10s;
-  }
-  [popover]:open {
-    opacity: 1;
   }
   :focus-within { border: 5px dashed red; }
   :focus { border: 5px solid lime; }
@@ -90,10 +81,6 @@
     t.add_cleanup(() => priorFocus.remove());
     return priorFocus;
   }
-  async function finishAnimationsAndVerifyHide(popover) {
-    await finishAnimations(popover);
-    assert_false(isElementVisible(popover),'After animations are finished, the popover should be hidden');
-  }
   function activateAndVerify(popover) {
     const testName = popover.getAttribute('data-test');
     promise_test(async t => {
@@ -113,7 +100,7 @@
       assert_equals(document.activeElement, expectedFocusedElement, `${testName} activated by popover.showPopover()`);
       popover.hidePopover();
       assert_equals(document.activeElement, priorFocus, 'prior element should get focus on hide, or if focus didn\'t shift on show, focus should stay where it was');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
 
       // Hit Escape:
       priorFocus.focus();
@@ -122,7 +109,7 @@
       assert_equals(document.activeElement, expectedFocusedElement, `${testName} activated by popover.showPopover()`);
       await sendEscape();
       assert_equals(document.activeElement, priorFocus, 'prior element should get focus after Escape');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
 
       // Move focus into the popover, then hit Escape:
       let containedButton = popover.querySelector('button');
@@ -134,7 +121,7 @@
         assert_equals(document.activeElement, containedButton);
         await sendEscape();
         assert_equals(document.activeElement, priorFocus, 'prior element should get focus after Escape');
-        await finishAnimationsAndVerifyHide(popover);
+        assert_false(isElementVisible(popover));
       }
 
       // Change the popover type:
@@ -145,7 +132,7 @@
       popover.popover = 'hint';
       assert_false(popover.matches(':open'), 'Changing the popover type should hide the popover');
       assert_equals(document.activeElement, priorFocus, 'prior element should get focus when the type is changed');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
       popover.popover = 'auto';
 
       // Remove from the document:
@@ -167,7 +154,7 @@
       dialog.showModal();
       assert_false(popover.matches(':open'), 'Opening a modal dialog should hide the popover');
       assert_not_equals(document.activeElement, priorFocus, 'prior element should *not* get focus when a modal dialog is shown');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
       dialog.close();
       dialog.remove();
 
@@ -181,7 +168,7 @@
       // Make sure Escape works in the invoker case:
       await sendEscape();
       assert_equals(document.activeElement, priorFocus, 'prior element should get focus after Escape (via invoker)');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
 
       // Make sure we can directly focus the (already open) popover:
       priorFocus.focus();
@@ -193,7 +180,7 @@
       button.click(); // Button is set to toggle the popover
       assert_false(popover.matches(':open'));
       assert_equals(document.activeElement, priorFocus, 'prior element should get focus on button-toggled hide');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
     }, "Popover focus test: " + testName);
 
     promise_test(async t => {
@@ -210,7 +197,7 @@
       await clickOn(button); // This will *not* light dismiss, but will "toggle" the popover.
       assert_false(popover.matches(':open'));
       assert_equals(document.activeElement, priorFocus, 'focus should return to the prior focus');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
 
       // Same thing, but the button is contained within the popover
       button.removeAttribute('popovertoggletarget');
@@ -227,7 +214,7 @@
       await clickOn(button);
       assert_false(popover.matches(':open'), 'clicking button should hide the popover');
       assert_equals(document.activeElement, priorFocus, 'Contained button should return focus to the previously focused element');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
 
       // Same thing, but the button is unrelated (no popovertoggletarget)
       button = document.createElement('button');
@@ -238,7 +225,7 @@
       await clickOn(button); // This will light dismiss the popover, focus the prior focus, then focus this button.
       assert_false(popover.matches(':open'), 'clicking button should hide the popover (via light dismiss)');
       assert_equals(document.activeElement, button, 'Focus should go to unrelated button on light dismiss');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
     }, "Popover button click focus test: " + testName);
 
     promise_test(async t => {
@@ -259,7 +246,7 @@
       assert_equals(document.activeElement, newFocus, 'focus should not change when prior focus is removed');
       popover.hidePopover();
       assert_not_equals(document.activeElement, priorFocus, 'focused element has been removed');
-      await finishAnimationsAndVerifyHide(popover);
+      assert_false(isElementVisible(popover));
       document.body.appendChild(priorFocus); // Put it back
 
       // Move the prior focus inside the (already open) popover
@@ -271,12 +258,7 @@
       assert_true(popover.contains(priorFocus));
       assert_true(popover.matches(':open'), 'popover should stay open');
       popover.hidePopover();
-      await waitForRender();
-      assert_true(isElementVisible(popover),'Animations should keep the popover visible');
-      assert_not_equals(getComputedStyle(popover).display,'none','Animations should keep the popover visible');
-      assert_equals(document.activeElement, priorFocus, 'focused element gets focused');
-      await finishAnimationsAndVerifyHide(popover);
-      assert_equals(getComputedStyle(popover).display,'none','Animations have ended, popover should be hidden');
+      assert_false(isElementVisible(popover));
       assert_not_equals(document.activeElement, priorFocus, 'focused element is display:none inside the popover');
       document.body.appendChild(priorFocus); // Put it back
     }, "Popover corner cases test: " + testName);
