hello, this sounds like a problem possibly caused by malware on your pc. please go to firefox > addons > extensions & remove any suspicious entries (especially the hosts 0.91.3 thingy, toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and run a full scan of your system with the security software that you have in place and different other tools like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

Note that your System Details List shows that you have a user.js file in the profile folder to initialize some prefs on each start of Firefox.

The user.js file is only present if you or other software has created it, so normally it wouldn't be there. You may want to check its content with a plain text editor if you didn't create this file yourself.

The user.js file is read each time you start Firefox and initializes preferences to the value specified in this file, so involved preferences can only be changed temporarily for the current session.

• http://kb.mozillazine.org/Preferences_not_saved

Stop FF extensions one by one except ones you are 100% sure off. Also, you might want to run anti-malware scan or investigate control panel applications.

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
• 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.

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

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

This user.js contains ONLY references to ZoneAlarm extensions.

In my case, the problem started just after a Firefox update. Coincidence??

I went very carefully through the "uninstall" list of software in the Control Panel and found an unfamiliar name (Lollipop) with the "Installed on" date matching the beginnings of my problem. I uninstalled it and have had no problem since. So I looked up their website and found a claim "Less disruptive than traditional advertisement". They must have a different definition of "less disruptive" than mine - I found the ads very disruptive - and always full screen. Anyhow problem solved.