Have you ever gone to hit ctrl-tab (to switch tabs) or ctrl-w (to close current tab) in Firefox and suddenly all your Firefox windows (even the one playing radio on another desktop) disappear? (I'm using Ubuntu and Gnome, but I get the impression this problem affects all Linux distros and all window managers.)
It must be old age making my fingers clumsier but I didn't even know ctrl-q did that until a few weeks ago. Yet I've done it a couple of times by accident recently, and when I did it today I decided Something Has To Be Done.
The solution is not just joyously simple, but I also learnt another cool function while I was there. First the solution: System|Preferences|Keyboard Shortcuts. Assign ctrl-q to do something; then Firefox never gets to see it. I assigned it to the calculator app which is nicely harmless.
I learnt this trick here, which also mentions that the same idea works in XCFE (go to keyboard panel). I'm betting KDE has something similar.
And the cool function? Looking through the other keyboard shortcuts I saw Alt+Print takes a screenshot of just the current window! You have no idea how many times I've clicked Print, then opened up Gimp to crop the screenshot to show just the window of interest. I'm now alternating between feeling very foolish and feeling very empowered.