Ok, so you have two options:

1. Disable Hardware Acceleration and leave it off until an update for your graphics driver comes out (it's the root cause of this issue). 2. Roll back to an older version of the graphics card driver and hopefully it fixes the issue.

My personal suggestion is to just leave Hardware acceleration disabled.

screenshot need to blurr some but i hope it help

it occures only in the firefox browser, in other everything is ok

Please see my reply, this is an issue with your graphics driver not working with Firefox's hardware acceleration. Turn off Hardware acceleration in firefox until your graphics card has an update.

will do this :)

I'm having the same issue and have not found solution yet

This is a known problem.

Here is the official bug page for this unresolved issue: https://bugzilla.mozilla.org/show_bug.cgi?id=837489

It appears to mostly affect AMD ATI HD 7xxx architecture. It started appearing with Firefox 18 I believe. It started appearing rarely with Catalyst 12.11 (maybe 12.10) and definitely with Catalyst 13.1 and 13.2. It is not limited to Windows 8.

Sometimes it doesn't appear for a while which makes you think that it does not affect the version of Windows/Catalyst/Firefox you are using but then it happens out of the blue later.

Here are some screen shots: http://www.overclockers.com/forums/showthread.php?t=726205

It does not affect Chrome or IE, it's Firefox (I think v18 and later) only.

It happen too in other pages like youtube. And there isn't only the web content, the GUI also goes crazy sometimes with those black squares...

https://bugzilla.mozilla.org/show_bug.cgi?id=837489 it's known bug, we need to be patient :)