Have you tested whether this affects any other browsers on your computer such as IE? ---- You may want to run some supplemental security scans. These two free tools are highly regarded: Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free SUPERAntiSpyware : http://www.superantispyware.com/ ---- In your comments, you said you have tried everything advised. Could you describe in more detail what you've tried? For example, to try to test whether one of your add-ons might be at fault, have you tried Firefox's Safe Mode? First, I recommend backing up your Firefox settings in case something goes wrong. See [[Backing up your information]]. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.) Next, restart Firefox in Firefox's [[Safe Mode]] using Help > Restart with Add-ons Disabled In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode." If the problem goes away, this points to one of your add-ons or a custom setting as the problem. Any luck?