Keyboard malfunction

Almost every time I alt-tab then return to the game, some vital keyboard keys are not working.  It is just a few keys, escape, return, sometimes the arrow keys.  They work perfectly well outside the game.  Anyone else got a similar problem?

Fixed.  It was being caused by windower, not Firefox as I suspected.  I was using Devleopment Build.  Reinstalled normal one and it seems fine now.