Bug 1385630 fix extension sidebar restore after app update, r=Gijs

MozReview-Commit-ID: IR0UDJgrp58

--HG--
extra : rebase_source : 6bb066650a94c3991e05c72ff3fb28cdb0e5a021

browser/base/content/browser-sidebar.js

@@ -235,6 +235,13 @@ var SidebarUI = {
       // refers to no longer exists, so we should assume this sidebar
       // panel has been uninstalled. (249883)
       this._box.removeAttribute("sidebarcommand");
+      // On a startup in which the startup cache was invalidated (e.g. app update)
+      // extensions will not be started prior to delayedLoad, thus the
+      // sidebarcommand element will not exist yet.  Store the commandID so
+      // extensions may reopen if necessary.  A startup cache invalidation
+      // can be forced (for testing) by deleting compatibility.ini from the
+      // profile.
+      this.lastOpenedId = commandID;
     }
   },
 

browser/components/extensions/ext-sidebarAction.js

@@ -134,11 +134,10 @@ this.sidebarAction = class extends ExtensionAPI {
                        (evt, tab) => { this.updateWindow(tab.ownerGlobal); });
 
     let install = this.extension.startupReason === "ADDON_INSTALL";
-    let upgrade = ["ADDON_UPGRADE", "ADDON_DOWNGRADE"].includes(this.extension.startupReason);
     for (let window of windowTracker.browserWindows()) {
       this.updateWindow(window);
       let {SidebarUI} = window;
-      if (install || (upgrade && SidebarUI.lastOpenedId == this.id)) {
+      if (install || SidebarUI.lastOpenedId == this.id) {
         SidebarUI.show(this.id);
       }
     }