Fix broken wheel zoom in Firefox

@damianavila, @kdodia, @tabchas  could use windows, linux testing testing. Works on safari, chrome, and firefox on OSX. 
> So, I dunno where the problem is, but I think we should merge this for now and get jquery-mousewheel working when we can.

I agree on this... it is a very ugly bug... we can come up with a better solution later.