FWIW, if you have session restore enabled, there is a checkbox to enable a quit warning waiting for you in the prefs (added a few months ago).

the problem is, I don't want to be annoyed by the warning when e.g. shutting down my computer or choosing to shut down firefox -- because of sessionrestore i do that a bunch anyway it's just frustrating to have it inadvertantly shut down with ctrl-q when you mistype

Yeah, I don't think there's any way to fix this (put differently, please contact me if you have a way for a computer to know whether you hit the shortcut on purpose or by accident :) ).

No that's the thing, I don't use ctrl-q on purpose. I close the browser with alt-f4 or the close button. Both are hard to do by accident. Ctrl-Q is next to some other common shortcuts

Yep. If I want to close the whole browser I use my mouse. It’s one of the few things I use the mouse for