Are you tired of hitting Ctrl+Q and quitting your whole Firefox session when you just meant to hit Ctrl+W to close a single tab?
Unless I am mistaken the latest versions of Firefox have the “Are you sure?” dialog for Ctrl+Q disabled by default. This is a terrible idea. On Windows and Mac you can use this extension to completely disable the shortcut: https://addons.mozilla.org/en-US/firefox/addon/disable-ctrl-q-and-cmd-q/
Unfortunately because Mozilla sucks you can’t use that add-on on Linux. Instead fix it by going to about:config and changing browser.showQuitWarning to true. This will enable the “Are you sure?” dialog so at least you can cancel closing the window.