the problem appear when i update from firefox 5.0 beta to 5.0 final i have install firefox 3.6.18, 5.0 and 6.0, but the problem still unsolved.

Probably caused by an incompatible extension.

http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes

i have started firefox in safe mode but the problem still occers in safe mode

Looks like a problem with the icons.
Those icons are either added by an extension or by a theme.

Does it really still happens in Save mode ?

• https://support.mozilla.com/kb/Safe+Mode

Are you using a special Windows theme?

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

In Firefox 4 you can use one of these to start in Safe mode:

• Help > Restart with Add-ons Disabled
• Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)

wonderful.

i have started in safe mode many times, but the problem is not solved. and i have just change my theme to win 7 default theme, and that problem is solved.

thank you very much. have a good day.