It did what I wanted most, to use Alt+Enter to open Full Screen, though I can't toggle Full Screen with the same combination...
Also, it would be a good idea to instruct somewhere how one can choose a bookmarklet to assign to a shortcut; I am not sure clicking

ok so weird thing that might be throughing people off is you type out the key,not press it, to set the shortcut. Also disabling 'alt' even in in the context of a page as far as highlighted text doesnt work. oddly though, remapping it to something like open new tab does.

nice little tool to customize Firefox
With this add-on, I can use the usual 'back' key assignment again :)

doesn't work

Firefox 94, it works. Shortcuts seem to only work in tabs that were opened after you saved the preference. So, if the extension doesn't appear to work, restart the browser and you should be good to go!

I use this to disable Option+Home, which immediately navigates "home" (blank tab) and loses any filled-in form data on the page. Was bumping that key combo all the time because the keys are adjacent on my Kinesis!

Too many permissions for a shortcut key addon

Only thing that works

doesnt work at all :/

It's dead - I wanted to match the shortcut for the sidebar to my 'normal' system sidebar shortcut, but I can't.

A little cumbersome to set up (e.g. I forgot to press the "Save shortcuts" button and thought it wasn't working), but after it's configured, it works perfectly! I finally was able to disable Firefox's bookmarks sidebar shortcut (Ctrl+B) which I activate by mistake all the time when trying to paste something (Ctrl+V).

It definitely works on Firefox 90 (the latest). Make sure you go to the GitHub page (linked in the add-on's description) and click the "Wiki" tab near the top to make sure you're setting it up right.

To the reviewers calling people idiots: if using the add on isn't intuitive its just as bad as having a non working add on. To access the activation options you need to press the ">" on the left for each short cut.

Adding some simple tutorial would have cleared up most of the bad reviews. How can you blame people for messing up when every other add on gives you an introduction? Anyway, great add on but read the github and make sure to activate the shortcut.

not working. running v89.0.6

edit: 3 years later still doesnt work

To people who are saying this doesn't work: once you are on the 'Manage Your Extensions' page, you just need to click the little gear button near the top, and then click 'manage extension shortcuts' at the bottom of the pop-up menu. The description should perhaps be updated, but the add-on works. Make sure what you want is on the list though; and this add-on can't override existing shortcuts.

In Firefox 89 there is just no option in the addon's preferences to add a shortcut. Doesn't work.

This extension works but the many people that are leaving 0 stars don't have a single brain cell to figure it out. Like Sahil who said alt+left did not work, I tried it and it worked fine. If you can't figure out how to use tech due to your own stupidity don't bother leaving negative reviews