Created attachment 542562 [details] [diff] [review] patch pageInfo.js never removes its callbacks (nor do the consumers remove themsevles), and browser_pageInfo.js doesn't remove its observer.
I don't really understand why the pageInfo.js changes are needed. How are those arrays special such that the need to be explicitly released on unload?
Anyone can add functions to the arrays. Add-ons do it and browser_bug517902.js does it.
I still don't see why that is a problem. Once the page info window goes away those references should die, whether you null them out explicitly or not.
browser_bug517902.js also holds a reference to the window. I don't know how reliably such cycles are resolved. It's also possible that the observer part alone gets rid of the leaks.
It looked like the pageInfo.js part fixed a bunch of about:blank leaks, but I'm getting unstable results now, so I just landed the browser_pageInfo.js fix. http://hg.mozilla.org/mozilla-central/rev/03f27e11397f