You can check for recently installed suspicious or unknown extensions. Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance). *Do NOT click the Reset button on the Safe Mode start window. *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes Extensions that do not have a "Remove" button are installed by other software and are not under control of the Firefox extension manager.<br /> Such globally installed extensions are usually found via a registry scan or are installed in a location that Firefox scans for installed extensions. * https://developer.mozilla.org/en/Adding_Extensions_using_the_Windows_Registry Extensions installed this way need to be removed via the settings (options/preferences) of the program that has added this extension or you need to uninstall this program via "Control Panel > Programs".<br /> In Firefox you an only disable such an extension.