Bug 731556 - When closing a hidden tab, don't attempt to animate it. r=gavin

--HG--
extra : rebase_source : 88451a3909c6191a6be8e83fc6c1e01ae325a451

browser/base/content/tabbrowser.xml

@@ -1526,6 +1526,7 @@
             if (!animate /* the caller didn't opt in */ ||
                 isLastTab ||
                 aTab.pinned ||
+                aTab.hidden ||
                 this._removingTabs.length > 3 /* don't want lots of concurrent animations */ ||
                 aTab.getAttribute("fadein") != "true" /* fade-in transition hasn't been triggered yet */ ||
                 window.getComputedStyle(aTab).maxWidth == "0.1px" /* fade-in transition hasn't moved yet */ ||