Could you try turning off a few Firefox settings. I'm not sure whether you need all of these, but no single one seems to solve the issue for everyone.

You usually need to restart Firefox in order for these changes to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

orange Firefox button or classic Tools menu > Options > Advanced

On the "General" mini-tab, Browsing section, uncheck the first 3 boxes:

1. Use autoscrolling
2. Use smooth scrolling
3. Use hardware acceleration when available

If you OK that and restart Firefox, is the issue resolved?

Thanks for the feedback but unfortunately disabling all 3 did not resolve the issue.

There are two Flash player settings you could change which might help: Flash's own hardware acceleration setting and the new protected mode for Windows Vista/7.

You can toggle the hardware acceleration setting using the steps in this article: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

To test whether the protected mode issue is relevant, you could temporarily disable this new feature. In the following article, scroll down to the "Last Resort" section: Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

The problem was with Flash Player's protected mode. This is the first I've heard of this new feature added to Flash. I guess I'll have to keep it disabled until the issue is resolved.

Cheers for your help jscher2000.

It's always the last thing you check. Thanks for reporting back.