Disable Cmd+Q in Firefox
There isn’t a number of situations where I pressed Cmd + Q and closed Firefox instead of Cmd + W and closing current tab and I have tried a lot of different things to stop it from custom keyboard shortcuts, to writing defaults in NSUserKeyEquivalents but without any success.
Now I have found solution.
There is experimental extension called Always Ask which solves this problem with simple popup asking you if you want to close Firefox or not.
Works like a charm.
Here is the link to it.