Bug 1412559 - Make the "confirm repost" prompt tab modal. r=bz

This is done to prevent malicious pages from abusing the feature
to lock up the browser.

MozReview-Commit-ID: 8Gf55nbMwCu

--HG--
extra : rebase_source : d3426bfef38a3dba27b1d1183b5f4427cbeb7436

docshell/base/nsDocShell.cpp

@@ -13559,6 +13559,12 @@ nsDocShell::ConfirmRepost(bool* aRepost)
     return rv;
   }
 
+  // Make the repost prompt tab modal to prevent malicious pages from locking
+  // up the browser, see bug 1412559 for an example.
+  if (nsCOMPtr<nsIWritablePropertyBag2> promptBag = do_QueryInterface(prompter)) {
+    promptBag->SetPropertyAsBool(NS_LITERAL_STRING("allowTabModal"), true);
+  }
+
   int32_t buttonPressed;
   // The actual value here is irrelevant, but we can't pass an invalid
   // bool through XPConnect.