Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause. If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Once you get the pop-up, just select ''Start in Safe Mode' (you may need to specify the Firefox installation path e.g. On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode.On Mac: Hold the option key while starting Firefox.On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.If Firefox is not running, you can start Firefox in Safe Mode as follows: If Firefox is open, you can restart in Firefox Safe Mode from the Help menu by clicking on the Restart with Add-ons Disabled. (If you're using an added theme, switch to the Default theme.) Firefox Safe Mode is a troubleshooting mode that turns off some settings and disables most add-ons (extensions and themes). Try Firefox Safe Mode to see if the problem goes away. You can also do a check for a rootkit infection with TDSSKiller. Make sure that you update each program to get the latest version of their databases before doing a scan. Please scan with all programs because each program detects different malware.

Do a malware check with several malware scanning programs on the Windows computer.