Ok, thanks. I had a similar problem, but in my case the reading of mousespeed was just much lower when a key was pressed. It must have something to do with incorrect event handling across all browsers, albeit to a slightly different degree. So I just took that mousespeed and in case of keypress I would multiply it by four or so. It's still noticeable, but much less. In your case, where there comes zero response, I would guess you are using integers that got rounded to zero. In any case have a look at my third person camera script in the mini3Dsoundengine.js project. It replaces the built in camera script of the coppercube engine, but should work with anything js in essence. I think I specifically remarked that part, where I multiply the mouse speed depending on keypresses. Well, it's a hack ^^