When it happen?

Every time when I'm browsing.

Try to scan computer with antivirus..maybe there is a malware on your computer...

It may be some sort of adware or malware. I append a standard reply about malware. *You did not list your Firefox extensions when posting the question. It may help if you paste a list of your extensions into your next reply. Troubleshooting Information lists these ** see [[Use the Troubleshooting Information page to help fix Firefox issues]] *Also you may wish to look in your Windows control panel and from there your list of installed programs, do you see anything you do not recognise ? *Additionally you my need to consider if you could have some toolbar or something taking over your searching ** see [[Remove a toolbar that has taken over your Firefox search or home page]] ------- 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: * [http://www.microsoft.com/security/scanner/default.aspx Microsoft Safety Scanner] * [http://www.malwarebytes.org/products/malwarebytes_free/ MalwareBytes' Anti-Malware] * [http://support.kaspersky.com/faq/?qid=208283363 TDSSKiller - AntiRootkit Utility] * [http://www.surfright.nl/en/hitmanpro/ Hitman Pro] * [http://www.eset.com/us/online-scanner/ ESET Online Scanner] * [http://www.bleepingcomputer.com/download/adwcleaner/ AdwCleaner: (for adware)] * [http://www.kaspersky.com/security-scan Kaspersky Free security scan] You need to use multiple and up-to-date tools as they will not all pick up the same things. [http://windows.microsoft.com/MSE Microsoft Security Essentials] is a good FREE 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. Did this fix your problems? Please report back to us!

I'm a techie. My system has all antivirus protection. Let me know what else to do.

Hello PeterBal, please try John99's [https://support.mozilla.org/en-US/questions/971847#answer-481313 reply] , each one of the above programs scans different malware. thank you