Hmm. I'm on Firefox/latest on Windows, and Ctrl-Q does nothing.
Is this a Linux thing?
I do accidentally close Firefox from time to time, though: The problem is that Shift-Control-W is "close window" instead of "close tab". Which makes sense, but sometimes I hit it by mistake, typically when I mean to hit Shift-Control-T. Don't know there's anything they could do to fix that.
I know I do hit Command-Q instead of Command-W almost every day on my Mac. I've installed a big keyboard macro application so that I can remap "Command-Q" to "nothing", I literally don't use it for anything else.
But this is worse. Pressing Command+W in Skype chat asks if you want to remove person from your favourites. At one specific version it actually closed the window. Go figure.