Well, I do use firefox, and haven't encountered this issue at all. (at least in previews)
When you say "I was able to duplicate it in firefox by just making the basic 'ghost hunter' demo game and using WASD simulated 8-way movement.", do you mean you export the ghost shooter demo or you execute it as preview and it "bugs" ?
Personally, I reach the quick find bar by pressing F3, and it never had interfered with controls in games so far.
I have an AZERTY keyboard and a French version of FF, maybe it is an issue with the english version (though I'd doubt it).
Really a strange behavior, it might be worth reporting to mozilla itself.
FF's most recent version is 17.0.1, make sure it is the version you're running (in case this "bug" had been corrected by the patch).