User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120228 Firefox/13.0a1 Build ID: 20120228031102 Steps to reproduce: STR: 0) Start a new profile with Nightly 1) Install the add-on about:ccdump to hunt the leak: https://addons.mozilla.org/en-US/firefox/addon/cycle-collector-analyzer/ 2) Open a 1st tab and go to about:ccdump 3) Open a 2nd tab (and go to http://www.nytimes.com/ e.g.) 4) Open a 3rd tab (and go to http://www.latimes.com/ e.g.) 5) Tear the 2nd tab 6) Tear the 3rd tab NB: at this step, you have 3 windows (about:ccdump, nytimes.com and latimes.com) 7) Grab the tab of the 2nd window (nytimes.com) and drop it on the left/right of the tab of the 3rd window (latimes.com) 8) Close the resulting window (confirm close if necessary) 9) Go back to tab about:ccdump, Run CC Analysis and search for nsDocument Results: nsDocument normal (XUL) chrome://browser/content/browser.xul leaks. Root objects: root nsNodeInfoManager root XPCVariant At step #7, you can grab the tab of the 2nd window and merge it with the 1st window and closing the 3rd window, same result. Idem with the 3rd window.

browser.xul was in the cc log for some time, but then disappeared. Did you run CC several times?

Yes, I ran CC several times. In addition, 'Run CC Analysis' in about:ccdump runs Firefox CC three times to clean up garbage.

What is "tearing" a tab?

Tab tearing allows you to pull any tab out of your Firefox window into a completely new window or pull any tab into another window.

Did someone try to reproduce it?

Sorry, I've forgotten to look at this. We marked it P3 because this seems like an uncommon operation.

This doesn't reproduce for me any more.

Loic, can you still reproduce?

(In reply to Nicholas Nethercote [:njn] from comment #8) > Loic, can you still reproduce? No. I guess you can close it.

Thanks for looking.