Sounds like a dose of Malware.

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
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Windows 8 has antivirus built-in already.

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

Did this fix your problems? Please report back to us!

If you get a pop-up message asking to update Firefox or plugins or scanning for malware then such a message is likely a scam and you should never respond to such an alert to avoid getting infected with malware.

• Only update Firefox via "Help > About" or by downloading and installing Firefox from the Mozilla server and never via a pop-up or link on a web page.
• Plugins should only be updated via the plugin itself or by visiting the home page of the plugin.

Roger_Ohio said

Just got this

It is a way some scammers are preying on inexperienced Firefox and or Windows users to get them to download this FAKE firefox_updater.exe to then infect their Windows.

I uploaded this .exe to virustotal and got this.

Detection ratio: 11 / 56 https://www.virustotal.com/en/file/28f844d7b7009694624a309c6a48bbd4a32a9f66479f8615e9bbbb3eb18c5041/analysis/1464481870/

So do not try to run this firefox_updater.exe