I see a link to McAfee on the status bar, so I think you probably have their "Site Advisor" and "Safe Search" installed which can be a problematical extension in Firefox. Try disabling it to see if it makes any difference: http://www.ehow.com/how_5803886_disable-mcafee-siteadvisor.html

That seems - up till now, after testing a while with many tabs open and a lot of switching and page loading - to solve the irritating problem! Thanks Xircal!

Page loading appears to be faster, too.

The strange 1px red borderline along the Firefox-window (see screenshot mentioned above) is still sticking around though; so this appears to be unrelated to the red screen issue?

For whom it may concern (as the procedure mentioned by Xircal - see link in his post - didn't work in my case, probably due to changes in McAfee AntiVirus Plus 2011):

1. Disable McAfee SiteAdvisor in Firefox via "Tools" - "Add-ons" -"Extensions" - click "Disable"-button.

2. Disable McAfee Site Advisor in Windows 7 by typing "msconfig" in the program-box just above Windows Start button after clicking that button, opening the program and:

- go to "Services"-tab and uncheck "McAfee Site Advisor Service";

- click "OK"-button;

- click "Yes"-button to restart the PC.

3. If necessary, restart Firefox (again) to get rid of the gray (= disabled) Site Advisor-button in de Extensions Toolbar

Are you using SandBoxie ?

No. Let's leave it at that.

I also had this problem - it turned out to be the IE tab add-on from http://www.ietab.net/.

Once I disabled that - the problem went away.

If you dont have IE tab then look to other add-ons - try disabling them one at a time until the issue is resolved, that will tell you what is causing the problem.

I have this problem as well, but it's nothing to do with any Firefox plugins...

A couple of days ago I used a download manager for a digital copy of Transformers 3, which had this peculiar red border around it for its windows. Since then I've tried everything, including uninstalling the manager to get rid of this red border, but nothing seems to work - my only conclusion is the Paramount website altered part of Firefox, and I now have to do a completely fresh installation to be rid of it...

I'll let you know how it turns out.

Well it appears my problem is not so simple; it's the new NVIDIA WHQL Driver. So I'm forced to either put up with a bug in the driver until the next update (which, for them, usually takes months), or rollback to the old driver I've been using for months to play Battlefield 3 without slowdowns...

Nice job NVIDIA.