Issue 6446 - Ignore emulated selectors if unchanged

include.preload.js

Index: include.preload.js
===================================================================
--- a/include.preload.js
+++ b/include.preload.js
@@ -30,16 +30,24 @@
   ["audio", "MEDIA"],
   ["video", "MEDIA"],
   ["frame", "SUBDOCUMENT"],
   ["iframe", "SUBDOCUMENT"],
   ["object", "OBJECT"],
   ["embed", "OBJECT"]
 ]);
 
+function haveSelectorsChanged(selectors, oldSelectors)
+{
+  if (selectors.length != oldSelectors.length)
+    return true;
+
+  return !selectors.every((selector, index) => selector == oldSelectors[index]);
+}
+
 function getURLsFromObjectElement(element)
 {
   let url = element.getAttribute("data");
   if (url)
     return [url];
 
   for (let child of element.children)
   {
@@ -342,16 +350,17 @@
 function ElemHide()
 {
   this.shadow = this.createShadowTree();
   this.styles = new Map();
   this.tracer = null;
   this.inline = true;
   this.inlineEmulated = true;
   this.emulatedPatterns = null;
+  this.emulatedSelectors = [];
 
   this.elemHideEmulation = new ElemHideEmulation(
     this.addSelectors.bind(this),
     this.hideElements.bind(this)
   );
 }
 ElemHide.prototype = {
   selectorGroupSize: 1024,
@@ -449,16 +458,21 @@
       ).join(", ");
       style.sheet.insertRule(selector + "{display: none !important;}",
                              style.sheet.cssRules.length);
     }
   },
 
   addSelectors(selectors, filters)
   {
+    if (!haveSelectorsChanged(selectors, this.emulatedSelectors))
+      return;
+
+    this.emulatedSelectors = selectors;
+
     if (this.inline || this.inlineEmulated)
     {
       // Insert the style rules inline if we have been instructed by the
       // background page to do so. This is usually the case, except on platforms
       // that do support user stylesheets via the browser.tabs.insertCSS API
       // (Firefox 53 onwards for now and possibly Chrome in the near future).
       // Once all supported platforms have implemented this API, we can remove
       // the code below. See issue #5090.