Hi, No idea how that happens, but for now you could still use Ctrl + T .... It could be the work of one of your extensions - would you try to disable them and see if that will bring the plus sign back ? A thing to try : Options => Customize, and look for a misplaced "+" button, or use the Restore Defaults button at the bottom of the Customize tab to reset toolbars back to their original layout. See : https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars Any luck ?