Bug 563337 - "Error: preview is undefined" and "this.preview is undef…

…ined" when closing the last tab with browser.tabs.closeWindowWithLastTab = false. r=gavin

--HG--
extra : rebase_source : 84f1e724f6a05b13c10b102de2df1007163ceb74

browser/base/content/tabbrowser.xml

@@ -1537,8 +1537,10 @@
             }
 
             this._removingTabs.push(aTab);
-
-            this.tabContainer.updateVisibility();
+            if (newTab)
+              this.addTab("about:blank", {skipAnimation: true});
+            else
+              this.tabContainer.updateVisibility();
 
             // We're committed to closing the tab now.
             // Dispatch a notification.
@@ -1594,8 +1596,6 @@
 
             // update the UI early for responsiveness
             aTab.collapsed = true;
-            if (aNewTab)
-              this.addTab("about:blank", {skipAnimation: true});
             this.tabContainer._fillTrailingGap();
             this._blurTab(aTab);