Bug 753807 - Land in comm-central Instantbird's changes to chat/ - Bio 1389 - Warning: reference to undefined property this._lastScrollHeight - fix bustage caused by 2eeb8a68d5a3, r=fqueze.

chat/content/convbrowser.xml

@@ -563,7 +563,7 @@
               return;
             }
 
-            if (!(_lastScrollHeight in this) ||
+            if (!("_lastScrollHeight" in this) ||
                 this._lastScrollHeight != this.scrollHeight ||
                 this._lastScrollWidth != this.scrollWidth) {
               // if the scrollheight changed, we are resizing the content area,