Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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Hello ahmed_atoon, are you able to open firefox in safe mode, by holding down the shift key while starting Firefox ?

if you can not open firefox in safe mode, see if your antivirus blocks firefox access, try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) and check firefox again.

(If works in Windows Safe mode then you have a problem with other software, like security software or maybe a system driver, that is running on your computer).

thank you

Thanks amitshree

I already use "Microsoft Security Essentials for Win7" Now I try Microsoft Safety Scanner