User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1 Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1 I open a bookmark folder that contains so many items that it reaches all the way down to the taskbar. After closing said folder, an afterimage of the portion that overlapped the taskbar gets stuck on the taskbar. (thx Gingerbread Man) Bug reproducible only with Windows 7 Basic Theme or Windows 7 Classic Theme. This test has been done with a created clean profile (no addons). Not reproducible with FF safe mode. Affected products: Firefox 4 and Firefox 4.0.1 Reproducible: Always Steps to Reproduce: 1. I created a new bookmark folder with 62 items inside 2. I moved this bookmark folder to the first place, before of the "Most visited" shortcut. 3. I open a bookmark folder that contains so many items that it reaches all the way down to the taskbar. 4. After closing said folder, an afterimage of the portion that overlapped the taskbar gets stuck on the taskbar. Bug reproducible only with Windows 7 Basic Theme or Windows 7 Classic Theme. This test has been done with a created clean profile (no addons). Not reproducible with FF safe mode. Affected products: Firefox 4 and Firefox 4.0.1 Actual Results: My conclusion is that firefox 4 is not compatible with windows 7 basic/classic theme if hardware acceleration is enabled Expected Results: Hardware acceleration should not interfere with Windows 7 Basic Theme or Windows 7 Classic Theme. There are some workarounds provided in this link: http://forums.mozillazine.org/viewtopic.php?f=9&t=2187413

Did you switch Windows visual style without restart Windows. If so, this duplicate of Bug 610713.

Yes, I switched Windows visual style without restart Windows. Please developers, can you delete attachments from this bug-thread? Thank you.

Thanks for the detailed bug report. I'm going to mark this as a dupe of bug 610713 due to comment 3 and comment 4; so that all progress on this can be tracked there.

Further discussion on this issue is best had in the bug it has been made a duplicate of.