User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12 I don't know how to reproduce this bug. I just open many many web pages and use Firefox as usual. And sometime, this issue happens. I'm not good at English. This bug is very strange. I can't describe this issue in English clearly, so I recorded a demo video with some English subtitles to show you this bug. Please download the video file from my Windows Live Skydrive: http://cid-3bffbda7b03370b7.office.live.com/self.aspx/.Public/Firefox%20Bug%20Demo%20Video/Firefox%20Bug%20Demo.avi Reproducible: Sometimes Steps to Reproduce: I can't find out how to reproduce this bug. Actual Results: Please watch my demo video.

Does it also occur in Safe Mode ? I see the DownloadThemAll add-on in the video. http://support.mozilla.com/en-US/kb/Safe+Mode

(In reply to comment #1) > Does it also occur in Safe Mode ? I see the DownloadThemAll add-on in the > video. > > http://support.mozilla.com/en-US/kb/Safe+Mode I haven't try this in Safe Mode yet. Because this issue isn't always occurs and I can't find out the exact reproduce steps. Today I have some work to do. Maybe tomorrow, I'll use Firefox in Safe Mode.

(In reply to comment #1) > Does it also occur in Safe Mode ? I see the DownloadThemAll add-on in the > video. > > http://support.mozilla.com/en-US/kb/Safe+Mode I have use Firefox in Safe Mode for 3 days, and this issue finally occur just now. I don't understand, how the mouse cursor affect the Firefox? I know a little about Windows Message Loop, but I don't understand how this issue occurs. Is it the XUL's bug or is the Javascript Engine's bug? Anyway, hope you fix this bug. Thank you!

Now my OS is Windows Vista x64, and I've been using Firefox 3.6 in Windows Vista over 3 months. It is strange that I never met this bug in this period. I doubt this bug is relate to the Graphic Card(ATI Mobility Radeon x1300) of my laptop or the Graphic Card Driver. Because my Graphic Card seems has some problem. In Windows Vista, if I use AMD-ATI's driver, it(Graphic Card or the driver) will cause Vista BSOD when I unplug the laptop's AC power line and plug it in back. This also happens in Windows 7. But if I use Windows Vista and it's built-in driver, everything is fine. So I doubt this bug is relate to the Graphic Card. Is it possible a Graphic Card hardware bug or driver bug make Firefox like that? Why?

Probably (?) duplicate of: Bug 627084 - UI becomes sluggish/does not redraw/repaint unless mouse is moved after long browsing sessions Bug 634163 - browser will not load pages or page content unless mouse cursor constantly moving.

The demo video is not accessible any more. OP didn't had this issue after changing OS and/or hardware.