All I can advise you is what I found using a Google Search.
I want you to reset firefox back to defaults, to do this I need you to do this
- At the top of the Firefox window, click the "Firefox" button,
- go over to the "Help" sub-menu
- (on Windows XP, click the Help menu at the top of the Firefox window) and select
- "Troubleshooting Information"
- Click the "Reset Firefox" button in the upper-right corner of the Troubleshooting Information page.
- click "Reset Firefox" in the confirmation window that opens.
- Firefox will close and be reset. When it's done. Click "Finish" and Firefox will open.
I moved this to the Malware Discussion area but not sure if it's really malware. Try running Stinger and Malwarebytes Free both found in the last link in my signature below as a precaution.