diff --git a/clients/extension/scripts/popup.js b/clients/extension/scripts/popup.js
index a73d73759e1a..d790373e3c8d 100644
--- a/clients/extension/scripts/popup.js
+++ b/clients/extension/scripts/popup.js
@@ -26,12 +26,11 @@ const STRINGS = BROWSER_BRAND === 'chrome' ? CHROME_STRINGS : FIREFOX_STRINGS;
 /**
  * Guaranteed context.querySelector. Always returns an element or throws if
  * nothing matches query.
- * @param {string} query
+ * @template {string} T
+ * @param {T} query
  * @param {ParentNode=} context
- * @return {HTMLElement}
  */
 function find(query, context = document) {
-  /** @type {?HTMLElement} */
   const result = context.querySelector(query);
   if (result === null) {
     throw new Error(`query ${query} not found`);
@@ -108,10 +107,9 @@ function fillDevToolsShortcut() {
 function readSettingsFromDomAndPersist() {
   const optionsEl = find('.section--options');
   // Save settings when options page is closed.
-  const checkboxes = /** @type {NodeListOf<HTMLInputElement>} */
-    (optionsEl.querySelectorAll('.options__categories input:checked'));
+  const checkboxes = optionsEl.querySelectorAll('.options__categories input:checked');
   const selectedCategories = Array.from(checkboxes).map(input => input.value);
-  const device = /** @type {HTMLInputElement} */ (find('input[name="device"]:checked')).value;
+  const device = find('input[name="device"]:checked').value;
 
   const settings = {
     selectedCategories,
@@ -155,8 +153,8 @@ async function initPopup() {
 
   const mainEl = find('main');
   const optionsEl = find('.button--configure');
-  const generateReportButton = /** @type {HTMLButtonElement} */ (find('.button--generate'));
-  const configureButton = /** @type {HTMLButtonElement} */ (find('.button--configure'));
+  const generateReportButton = find('button.button--generate');
+  const configureButton = find('button.button--configure');
   const psiDisclaimerEl = find('.psi-disclaimer');
   const errorMessageEl = find('.errormsg');
   const optionsFormEl = find('.options__form');
diff --git a/lighthouse-core/gather/fetcher.js b/lighthouse-core/gather/fetcher.js
index cd13313e8873..94c2660e908f 100644
--- a/lighthouse-core/gather/fetcher.js
+++ b/lighthouse-core/gather/fetcher.js
@@ -143,7 +143,6 @@ class Fetcher {
      */
     /* c8 ignore start */
     function injectIframe(src) {
-      /** @type {HTMLIFrameElement} */
       const iframe = document.createElement('iframe');
       // Try really hard not to affect the page.
       iframe.style.display = 'none';
diff --git a/lighthouse-core/gather/gatherers/dobetterweb/tags-blocking-first-paint.js b/lighthouse-core/gather/gatherers/dobetterweb/tags-blocking-first-paint.js
index 9fc13ea49202..8ef9d294f4e2 100644
--- a/lighthouse-core/gather/gatherers/dobetterweb/tags-blocking-first-paint.js
+++ b/lighthouse-core/gather/gatherers/dobetterweb/tags-blocking-first-paint.js
@@ -61,13 +61,10 @@ async function collectTagsThatBlockFirstPaint() {
   try {
     /** @type {Array<LinkTag>} */
     const linkTags = [...document.querySelectorAll('link')]
-      .filter(/** @return {tag is HTMLLinkElement} */ tag => {
-        if (tag.tagName !== 'LINK') return false;
-
+      .filter(linkTag => {
         // Filter stylesheet/HTML imports that block rendering.
         // https://www.igvita.com/2012/06/14/debunking-responsive-css-performance-myths/
         // https://www.w3.org/TR/html-imports/#dfn-import-async-attribute
-        const linkTag = /** @type {HTMLLinkElement} */ (tag);
         const blockingStylesheet = linkTag.rel === 'stylesheet' &&
           window.matchMedia(linkTag.media).matches && !linkTag.disabled;
         const blockingImport = linkTag.rel === 'import' && !linkTag.hasAttribute('async');
@@ -87,10 +84,7 @@ async function collectTagsThatBlockFirstPaint() {
 
     /** @type {Array<ScriptTag>} */
     const scriptTags = [...document.querySelectorAll('head script[src]')]
-      .filter(/** @return {tag is HTMLScriptElement} */ tag => {
-        if (tag.tagName !== 'SCRIPT') return false;
-
-        const scriptTag = /** @type {HTMLScriptElement} */ (tag);
+      .filter(scriptTag => {
         return (
           !scriptTag.hasAttribute('async') &&
           !scriptTag.hasAttribute('defer') &&
diff --git a/lighthouse-core/report/html/renderer/category-renderer.js b/lighthouse-core/report/html/renderer/category-renderer.js
index 58af7d068526..1fe8f5884113 100644
--- a/lighthouse-core/report/html/renderer/category-renderer.js
+++ b/lighthouse-core/report/html/renderer/category-renderer.js
@@ -170,7 +170,7 @@ class CategoryRenderer {
   /**
    * @param {LH.ReportResult.Category} category
    * @param {Record<string, LH.Result.ReportGroup>} groupDefinitions
-   * @return {Element}
+   * @return {DocumentFragment}
    */
   renderCategoryHeader(category, groupDefinitions) {
     const tmpl = this.dom.cloneTemplate('#tmpl-lh-category-header', this.templateContext);
@@ -184,7 +184,7 @@ class CategoryRenderer {
       this.dom.find('.lh-category-header__description', tmpl).appendChild(descEl);
     }
 
-    return /** @type {Element} */ (tmpl.firstElementChild);
+    return tmpl;
   }
 
   /**
@@ -336,8 +336,7 @@ class CategoryRenderer {
     // Cast `null` to 0
     const numericScore = Number(category.score);
     const gauge = this.dom.find('.lh-gauge', tmpl);
-    /** @type {?SVGCircleElement} */
-    const gaugeArc = gauge.querySelector('.lh-gauge-arc');
+    const gaugeArc = this.dom.find('circle.lh-gauge-arc', gauge);
 
     if (gaugeArc) this._setGaugeArc(gaugeArc, numericScore);
 
diff --git a/lighthouse-core/report/html/renderer/dom.js b/lighthouse-core/report/html/renderer/dom.js
index 8b564606772b..18f2db42b85b 100644
--- a/lighthouse-core/report/html/renderer/dom.js
+++ b/lighthouse-core/report/html/renderer/dom.js
@@ -218,7 +218,6 @@ class DOM {
    * @param {ParentNode} context
    */
   find(query, context) {
-    /** @type {?import('typed-query-selector/parser').ParseSelector<T>} */
     const result = context.querySelector(query);
     if (result === null) {
       throw new Error(`query ${query} not found`);
@@ -233,7 +232,6 @@ class DOM {
    * @param {ParentNode} context
    */
   findAll(query, context) {
-    /** @type {Array<import('typed-query-selector/parser').ParseSelector<T>>} */
     const elements = Array.from(context.querySelectorAll(query));
     return elements;
   }
diff --git a/lighthouse-core/report/html/renderer/logger.js b/lighthouse-core/report/html/renderer/logger.js
index 864c1b0ab87b..9044dac93586 100644
--- a/lighthouse-core/report/html/renderer/logger.js
+++ b/lighthouse-core/report/html/renderer/logger.js
@@ -24,7 +24,6 @@ class Logger {
    * @param {Element} element
    */
   constructor(element) {
-    /** @type {Element} */
     this.el = element;
     this._id = undefined;
   }
diff --git a/lighthouse-core/report/html/renderer/report-renderer.js b/lighthouse-core/report/html/renderer/report-renderer.js
index 002e567c9ceb..3f608125e607 100644
--- a/lighthouse-core/report/html/renderer/report-renderer.js
+++ b/lighthouse-core/report/html/renderer/report-renderer.js
@@ -83,7 +83,7 @@ class ReportRenderer {
     const el = this._dom.cloneTemplate('#tmpl-lh-heading', this._templateContext);
     const domFragment = this._dom.cloneTemplate('#tmpl-lh-scores-wrapper', this._templateContext);
     const placeholder = this._dom.find('.lh-scores-wrapper-placeholder', el);
-    /** @type {HTMLDivElement} */ (placeholder.parentNode).replaceChild(domFragment, placeholder);
+    placeholder.replaceWith(domFragment);
     return el;
   }
 
diff --git a/lighthouse-core/report/html/renderer/report-ui-features.js b/lighthouse-core/report/html/renderer/report-ui-features.js
index 15386ed3936c..db281706c667 100644
--- a/lighthouse-core/report/html/renderer/report-ui-features.js
+++ b/lighthouse-core/report/html/renderer/report-ui-features.js
@@ -238,8 +238,7 @@ class ReportUIFeatures {
     ];
 
     // Get all tables with a text url column.
-    /** @type {Array<HTMLTableElement>} */
-    const tables = Array.from(this._document.querySelectorAll('.lh-table'));
+    const tables = Array.from(this._document.querySelectorAll('table.lh-table'));
     const tablesWithUrls = tables
       .filter(el =>
         el.querySelector('td.lh-table-column--url, td.lh-table-column--source-location'))
@@ -335,8 +334,7 @@ class ReportUIFeatures {
     for (const rowEl of rowEls) {
       if (rowEl.classList.contains('lh-sub-item-row')) continue;
 
-      /** @type {HTMLElement|null} */
-      const urlItem = rowEl.querySelector('.lh-text__url');
+      const urlItem = rowEl.querySelector('div.lh-text__url');
       if (!urlItem) continue;
 
       const datasetUrl = urlItem.dataset.url;
@@ -834,11 +832,11 @@ class DropDown {
 
   /**
    * @param {Array<Node>} allNodes
-   * @param {?Node=} startNode
-   * @returns {Node}
+   * @param {?HTMLElement=} startNode
+   * @returns {HTMLElement}
    */
   _getNextSelectableNode(allNodes, startNode) {
-    const nodes = allNodes.filter((node) => {
+    const nodes = allNodes.filter(/** @return {node is HTMLElement} */ (node) => {
       if (!(node instanceof HTMLElement)) {
         return false;
       }
@@ -865,21 +863,21 @@ class DropDown {
   }
 
   /**
-   * @param {?Element=} startEl
+   * @param {?HTMLElement=} startEl
    * @returns {HTMLElement}
    */
   _getNextMenuItem(startEl) {
     const nodes = Array.from(this._menuEl.childNodes);
-    return /** @type {HTMLElement} */ (this._getNextSelectableNode(nodes, startEl));
+    return this._getNextSelectableNode(nodes, startEl);
   }
 
   /**
-   * @param {?Element=} startEl
+   * @param {?HTMLElement=} startEl
    * @returns {HTMLElement}
    */
   _getPreviousMenuItem(startEl) {
     const nodes = Array.from(this._menuEl.childNodes).reverse();
-    return /** @type {HTMLElement} */ (this._getNextSelectableNode(nodes, startEl));
+    return this._getNextSelectableNode(nodes, startEl);
   }
 }
 
diff --git a/lighthouse-treemap/app/src/util.js b/lighthouse-treemap/app/src/util.js
index b5ceb79665d4..e80c9cd99f04 100644
--- a/lighthouse-treemap/app/src/util.js
+++ b/lighthouse-treemap/app/src/util.js
@@ -52,12 +52,11 @@ class TreemapUtil {
   /**
    * Guaranteed context.querySelector. Always returns an element or throws if
    * nothing matches query.
-   * @param {string} query
+   * @template {string} T
+   * @param {T} query
    * @param {ParentNode=} context
-   * @return {HTMLElement}
    */
   static find(query, context = document) {
-    /** @type {?HTMLElement} */
     const result = context.querySelector(query);
     if (result === null) {
       throw new Error(`query ${query} not found`);
diff --git a/lighthouse-viewer/app/src/lighthouse-report-viewer.js b/lighthouse-viewer/app/src/lighthouse-report-viewer.js
index 51b9265a9716..63dc87c0db03 100644
--- a/lighthouse-viewer/app/src/lighthouse-report-viewer.js
+++ b/lighthouse-viewer/app/src/lighthouse-report-viewer.js
@@ -12,12 +12,11 @@
 /**
  * Guaranteed context.querySelector. Always returns an element or throws if
  * nothing matches query.
- * @param {string} query
+ * @template {string} T
+ * @param {T} query
  * @param {ParentNode} context
- * @return {HTMLElement}
  */
 function find(query, context) {
-  /** @type {?HTMLElement} */
   const result = context.querySelector(query);
   if (result === null) {
     throw new Error(`query ${query} not found`);
@@ -67,7 +66,7 @@ class LighthouseReportViewer {
     gistUrlInput.addEventListener('change', this._onUrlInputChange);
 
     // Hidden file input to trigger manual file selector.
-    const fileInput = find('#hidden-file-input', document);
+    const fileInput = find('input#hidden-file-input', document);
     fileInput.addEventListener('change', e => {
       if (!e.target) {
         return;
@@ -283,8 +282,7 @@ class LighthouseReportViewer {
     return new Promise((resolve, reject) => {
       const reader = new FileReader();
       reader.onload = function(e) {
-        const readerTarget = /** @type {?FileReader} */ (e.target);
-        const result = /** @type {?string} */ (readerTarget && readerTarget.result);
+        const result = /** @type {?string} */ (e.target && e.target.result);
         if (!result) {
           reject('Could not read file');
           return;
diff --git a/types/externs.d.ts b/types/externs.d.ts
index 9cdc87fe2258..3ceab1690d98 100644
--- a/types/externs.d.ts
+++ b/types/externs.d.ts
@@ -7,6 +7,9 @@
 import _Crdp from 'devtools-protocol/types/protocol';
 import _CrdpMappings from 'devtools-protocol/types/protocol-mapping'
 
+// Import for side effects improving types of querySelector/querySelectorAll.
+import 'typed-query-selector';
+
 declare global {
   // Augment Intl to include
   // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/getCanonicalLocales