Bug 1255511 - Skip beforeunload prompts once nsIAppStartup shuttingDown returns true. r?Gijs When the application is asked to quit, all windows are checked to see if they can close (which will spawn the permit unload dialogs). Once the user grants the quit via the permit unload dialogs, nsIAppStartup returns true for the shuttingDown attribute, and we know that all windows allowed the shutdown to occur. This means that we don't have to show the permitUnload dialogs again when SessionStore attempts to close the windows when it does its final async window flush during the quit-application-granted observer topic. MozReview-Commit-ID: DOy8ljngnTd

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -6119,17 +6119,17 @@ var IndexedDBPromptHelper = {
     timeoutId = setTimeout(timeoutNotification, firstTimeoutDuration);
   }
 };
 
 function CanCloseWindow()
 {
   // Avoid redundant calls to canClose from showing multiple
   // PermitUnload dialogs.
-  if (window.skipNextCanClose) {
+  if (Services.startup.shuttingDown || window.skipNextCanClose) {
     return true;
   }
 
   for (let browser of gBrowser.browsers) {
     let {permitUnload, timedOut} = browser.permitUnload();
     if (timedOut) {
       return true;
     }