Hi. Try using Firefox in safe mode. Click the menu button , click help and select Restart with Add-ons Disabled.Firefox will start up with the Firefox Safe Mode dialog.

If this doesn't work, try starting Firefox in Safe Mode by holding onto the shift key while starting Firefox.

HOPE THIS HELPED :)

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.