Hi, You could try to close individual windows using the X button on the top right and the last window via '''File''' ('''Alt''' + '''F''') > '''Exit''' or Firefox button > '''Exit'''. If the problem persists please check if this happens in [https://support.mozilla.com/en-US/kb/Safe%20Mode Safe Mode]. Safe mode disables the installed '''Extensions''', and themes ('''Appearance''') in '''Tools''' ('''Alt''' + '''T''') > '''Add-ons'''. Hardware acceleration is also temporarily disabled - the manual setting is '''Tools''' > '''Options''' > '''Advanced''' > '''General''' > [https://support.mozilla.org/en-US/kb/Options%20window%20-%20Advanced%20panel?as=u '''Use hardware acceleration when available''']. All these settings/options/add-ons can also be individually or collectively disabled/enabled/changed in Firefox normal mode to check if an extension, theme, option or hardware acceleration is causing issues. Disabling/enabling hardware acceleration, and some types of add-ons in normal mode may require a Firefox restart. [http://support.mozilla.com/en-US/kb/Uninstalling+add-ons Uninstalling Add-ons] [http://kb.mozillazine.org/Uninstalling_toolbars Uninstalling Toolbars] [https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes Troubleshooting Extensions and Themes] [http://kb.mozillazine.org/Problematic_extensions Problematic Extensions] [https://support.mozilla.org/en-US/kb/Options%20window Options] You can also check this in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. If the new profile is okay, you can then [https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems Reset Firefox] on the old (previous) profile via '''Help''' ('''Alt''' + '''H''') > '''Troubleshooting Information'''.