use MutationObserver to track dom node additions.

src/gmail.js

@@ -739,7 +739,7 @@
                 "false": !1,
                 "null": null
             };
         each(params.replace(/\+/g, " ").split("&"), function (v, j) {
             var param = v.split("="),
                 key = decodeURIComponent(param[0]),
                 val,
@@ -790,7 +790,7 @@
         }
     };
 
     api.tools.parse_actions = function(params, xhr) {
 
         // upload_attachment event - if found, don"t check other observers. See issue #22
         if(params.url.act === "fup" || params.url.act === "fuv" || params.body_is_object) {
@@ -1908,7 +1908,7 @@
         }
 
         let parsedResponse = [];
         let originalResponse = response;
         try {
             // gmail post response structure
             // )}]"\n<datalength><rawData>\n<dataLength><rawData>...
@@ -2087,7 +2087,7 @@
         const win = api.helper.get_xhr_window();
 
         api.tools.patch(win.XMLHttpRequest.prototype.open, (orig) => {
             win.XMLHttpRequest.prototype.open = function (method, url, async, user, password) {
                 var out = orig.apply(this, arguments);
                 this.xhrParams = {
                     method: method.toString(),
@@ -2353,7 +2353,7 @@
             // if an object of actions (triggered events of format { event: [response] }) is passed, check if any of these are bound
             if(typeof action === "object") {
                 var match = false;
                 $.each(action,function(key,response){
                     if(typeof api.tracker.watchdog[type][key] === "object") match = true;
                 });
                 return match;
@@ -2389,7 +2389,7 @@
                     delete api.tracker.watchdog[type][action];
                 }
             } else {
                 $.each(api.tracker.watchdog[type], function(act,callbacks) {
                     if(typeof api.tracker.watchdog[type][act] === "object") {
                         api.tracker.bound[act] -= api.tracker.watchdog[type][act].length;
                         api.tracker.bound[type] -= api.tracker.watchdog[type][act].length;
@@ -2672,13 +2672,6 @@
                 api.tracker.observing_dom = true;
                 //api.tracker.dom_watchdog = {}; // store passed observer callbacks for different DOM events
 
-                // this listener will check every element inserted into the DOM
-                // for specified classes (as defined in api.tracker.dom_observers above) which indicate
-                // related actions which need triggering
-                $(window.document).on("DOMNodeInserted", function(e) {
-                    api.tools.insertion_observer(e.target, api.tracker.dom_observers, api.tracker.dom_observer_map);
-                });
-
                 // recipient_change also needs to listen to removals
                 var mutationObserver = new MutationObserver(function(mutations) {
                     for (var i = 0; i < mutations.length; i++) {
@@ -2697,6 +2690,15 @@
                                 api.observe.trigger_dom(observer, $(mutation.target), handler);
                             }
                         }
+
+                        // this listener will check every element inserted into the DOM
+                        // for specified classes (as defined in api.tracker.dom_observers above) which indicate
+                        // related actions which need triggering
+                        var addedNodes = mutation.addedNodes;
+                        for (var k = 0; k < addedNodes.length; k++) {
+                            var addedNode = addedNodes[k];
+                            api.tools.insertion_observer(addedNode, api.tracker.dom_observers, api.tracker.dom_observer_map);
+                        }
                     }
                 });
                 mutationObserver.observe(document.body, {subtree: true, childList: true});
@@ -2744,7 +2746,7 @@
 
     // observes every element inserted into the DOM by Gmail and looks at the classes on those elements,
     // checking for any configured observers related to those classes
     api.tools.insertion_observer = function(target, dom_observers, dom_observer_map, sub) {
         //console.log("insertion", target, target.className);
         if(!dom_observer_map) return;