That may be related to Firefox switching to hardware acceleration. If the screen buffer that is used isn't empty then you may see older content of it displayed until that screen buffer is cleared.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

If disabling hardware acceleration works then check if there is an update available for your graphics display driver.

I have this problem also. I disabled 'hardware acceleration' but it made no difference. I have nothing to do with McAfee loaded and I am not using Sandboxie. The screen only appears at initial start-up of Firefox 7.0.1 . I doesn't seem to be causing any problems it's just the fact that it never used to be there.

Any other suggestions gratefully accepted.

Thanks.

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.