How long has this been happening? Have you made any changes since it started? Have you tried running a virus scan (best to run in safe mode)? First select to update your anti-virus software, then close and reopen in safe mode. Then run it in safe mode. Edit: I just noticed a post below by 'butters9' that was answered. Does the solution apply to your situation? See link to the post below: https://support.mozilla.com/en-US/questions/893076