Bug 940262 - [Australis] Hide .tab-background in the early tabopen animation phase and show it after a short offset r=dao

From b7ac00600af262042d076ba5ac04138eb4ee0418 Mon Sep 17 00:00:00 2001
Bug 932898 - Bring back the shutdown leak detector r=ted

From 246109686e62e3231ccba74a84adaa0774f2a1af Mon Sep 17 00:00:00 2001