Bug 1561970 - BrowserTabParent should ignore browser elements related to non-tab extension pages. r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D37051

--HG--
extra : moz-landing-system : lando

browser/actors/BrowserTabParent.jsm

@@ -13,6 +13,7 @@ class BrowserTabParent extends JSWindowActorParent {
     }
 
     let gBrowser = browser.ownerGlobal.gBrowser;
+
     if (!gBrowser) {
       // Note: gBrowser might be null because this message might be received
       // from the extension process. There's still an embedderElement involved,
@@ -22,6 +23,15 @@ class BrowserTabParent extends JSWindowActorParent {
       return;
     }
 
+    if (!gBrowser.tabpanels || !gBrowser.tabpanels.contains(browser)) {
+      // Note: This is ignoring browser elements related to extension pages that are not loaded
+      // as a browser tab (like sidebars, devtools panels and options pages embedded into
+      // about:addons, browserAction and pageAction popup panels.
+      // (Ideally we could call gBrowser.getTabForBrowser, but it returns undefined early in
+      // the tab browser creation and we would ignore browsers related to newly created tabs).
+      return;
+    }
+
     switch (message.name) {
       case "Browser:WindowCreated": {
         gBrowser.announceWindowCreated(browser, message.data.userContextId);