I know what it's like, your sitting there at work bored out of your mind thinking 'Man, I wish I could play a browser version of Doom'.
I think it all the time, so make sure your Adobe Flash is up to date and have a trip down memory lane on me!
Space bar = Shoot
A,W,S,D = Move
Q,E = Side Step
Shift = Run
Ctrl = Use door/button
(Where it says 'Play' on the first screen you have to click there)