As you probably know, in Firefox there is unfortunately no way to configure existing shortcuts. All I found is the keyconfig add-on, that seems really old and very hard to configure (there is no UI, only about:config). That’s why I finally decided to write an add-on with a neat UI (not only) for casual users in mind. I would love to see such a feature directly delivered with Firefox some day because it enables you not only to modify shortcuts to your needs but also to easily discover new ones you haven’t heard of, yet.
The add-on’s current version is 0.5.8 – so I already invested a decent amount of time. Unfortunately I’m still waiting for full review from the AMO team as their backlog is pretty high after the Firefox 4 release. If you have any thoughts or bugs feel free to comment.