Can I add a keyboard shortcut to close all other tabs?

Bonjour

Customize keyboard shortcuts in Firefox https://support.mozilla.org/en-US/kb/customize-keyboard-shortcuts-firefox

A space for users to give product feedback https://support.mozilla.org/en-US/kb/what-mozilla-connect

I read that before asking the question. It does not answer the question.

You're right, that article doesn't really answer this one. I checked about:keyboard in my own Firefox and I can change dozens of shortcuts there, but I couldn't find a Close Other Tabs entry to assign, so as far as I can tell there is no built-in shortcut for that action yet. What I do instead is right-click the tab I want to keep and choose Close Other Tabs, which is the quickest built-in way I have found. If you want it as a proper shortcut, I would suggest posting it as an idea on Mozilla Connect, since that is where the team collects this kind of feature request.