If you're fed up by websites installing absurd shortcuts like e.g. ctrl+k (yes, I'm looking at you, GitHub).

Just set permissions.default.shortcuts to 2 (3 doesn't seem to work for me) in about:config, and you're finally free.

Disclaimer: I just tested that moments ago, so maybe there's downsides to this, but for now it just felt amazing stopping worrying whether ctrl+k will do what I want or a random useless action.

A simple way to force Firefox/Iceweasel to clear its local DNS cache.