Open the url testcase. When I hover over the tab of that of that image document, I get a severe slow-down of the mouse cursor and cpu creeps up to almost 100%. Also, switching tabs has become slower and more cpu intensive, when one of the tabs contains that image document. I've seen this happening with a lot more images, this bug, but not with all images. This isn't an issue with small images. I tend to think: the larger the image, the slower the cursor and the more cpu is used. I'm using NVidia TNT2 M64 32 MB 16 bit color depth, Duron 800MHz. This might very well be a Core GFX:Win32 issue (especially a problem with NVidia cards), since this bug was introduced with the fix for bug 125998. That fix probably just exposed this bug. CC-ing you Arron, I hope you don't mind.

This doesn't happen with all images, by the way. It seems to matter what dimensions the image have, see here: http://www.wargers.org/test/mozilla/bug285141/cat1280x1024.jpg http://www.wargers.org/test/mozilla/bug285141/cat975x635.jpg The first one is larger, but doesn't cause this bug. The second one is larger, but causes the bug.

I saw this too on this page: http://img123.echo.cx/img123/9050/bloggerscrewed9dd.png but not on this page: http://img136.echo.cx/my.php?image=website5wq.jpg So possibly it has something to do with the miniature that Firefox has generated for the tab? I see this only on a notebook with a 900 Mhrz CPU; on a computer with a faster CPU I don't see this problem.

Also mentioned here: http://forums.mozillazine.org/viewtopic.php?t=283815

Hmm, actually bug 304561 sounds the same as this bug, but I think the fix of that bug is probably not enough to fix the bug.

Bug 305986 should take care of this on trunk.

With current Nightly (Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:21.0) Gecko/20130212 Firefox/21.0), I'm unable to reproduce this. Marking RESOLVED WORKSFORME. Please re-open if this is still an issue.