After several hundred tests in mochitest-browser-chrome test runs, I see ~1k observers for author-style-disabled-changed in about:memory. The only place those are added is here: http://mxr.mozilla.org/mozilla-central/source/browser/components/sessionstore/content/content-sessionStore.js#323 and they are never removed. They are weak observers, but that probably doesn't matter either, as that event is rather rare. It looks like we'd really need to be notified when a frame script is destructed, so we could do some cleanup, but there's no such notification currently.

Comment on attachment 8361973 [details] [diff] [review] 0001-Bug-961106-Remove-observers-on-frame-script-unload.patch Review of attachment 8361973 [details] [diff] [review]: ----------------------------------------------------------------- It might be useful to comment that the gFrameTree observers don't need to be removed because gFrameTree will die with the content script, and it holds the observers. And the privacy transition thing is okay because it's on the docshell, which will die along with the tab. ::: browser/components/sessionstore/content/content-sessionStore.js @@ +342,4 @@ > */ > let PageStyleListener = { > init: function () { > Services.obs.addObserver(this, "author-style-disabled-changed", true); Do you mind changing the "weak" parameter to false. I don't think that setting it to true is helping us, and I think it would be good to reduce the number of places where we use weak observers.

Is this definitely new to FF27? Should we be looking for a regression range here?

Bug 930967 is what regressed this.

Yeah, this has been introduced with Fx 28. (In reply to Bill McCloskey (:billm) from comment #3) > It might be useful to comment that the gFrameTree observers don't need to be > removed because gFrameTree will die with the content script, and it holds > the observers. And the privacy transition thing is okay because it's on the > docshell, which will die along with the tab. Good idea. > Do you mind changing the "weak" parameter to false. I don't think that > setting it to true is helping us, and I think it would be good to reduce the > number of places where we use weak observers. Will do.

Comment on attachment 8361973 [details] [diff] [review] 0001-Bug-961106-Remove-observers-on-frame-script-unload.patch [Approval Request Comment] Bug caused by (feature/regressing bug #): bug 930967 User impact if declined: Observers are leaked when closing tabs. Testing completed (on m-c, etc.): Will be in tomorrow's nightly. Risk to taking this patch (and alternatives if risky): Small low-risk patch. String or IDL/UUID changes made by this patch: None.