As Panorama is slated for removal in the not too distant future (and not only because of that) it would be great if the Panorama tests would clean up after themselves and dispose the Panorama iframe. While working on reducing uninterruptible reflows affecting the tabopen animation, I came across a reflow that is caused by a .getBoundingClientRect() call in the Panorama iframe: > "iQClass_height@chrome://browser/content/tabview.js|" + > "GroupItem_getContentBounds@chrome://browser/content/tabview.js|" + > "GroupItem_shouldStack@chrome://browser/content/tabview.js|" + > "GroupItem_arrange@chrome://browser/content/tabview.js|" + > "GroupItem_add@chrome://browser/content/tabview.js|" + > "GroupItems_newTab@chrome://browser/content/tabview.js|" + > "TabItem__reconnect@chrome://browser/content/tabview.js|" + > "TabItem@chrome://browser/content/tabview.js|" + > "TabItems_link@chrome://browser/content/tabview.js|" + > "@chrome://browser/content/tabview.js|" + > "addTab@chrome://browser/content/tabbrowser.xml|" Panorama is registering a new tab when it's opened. A call that flushes layout in the iframe will also flush layout in the parent document (i.e. the browser window) if it's dirty. One solution would be to just add this stack trace to the list of expected reflows but I think the better way would be to unload the Panorama iframe so that it doesn't listen for TabOpen events anymore.

Comment on attachment 758539 [details] [diff] [review] make Panorama tests clean up after themselves I'm not too fond of resetting everything between tests, as unexpectedly interacting tests can expose interesting bugs. But since panorama is slated for removal, I don't really care.

Let's not do this for now and keep Panorama test coverage.