I may be reporting this bug in the wrong component, or it might be a Firefox-specific bug and not on the platform. The basic issue is this: I'm using Apple's Mighty Mouse, and I swipe my finger up to scroll to the top of a page. A moment later, I hold down "ctrl-tab" to switch to a different window, at which point Firefox first starts zooming into the window, eventually switches tabs, and then continues zooming into the tab i've switched to. I have to press ctrl-0 to reset the zoom level to its default. What I think is going on is this: the finger-swipe spawns a bunch of mousewheel events that are processed over the next few seconds (I have no idea if the OS is sending the events over time, or if Firefox's code is processing them over an extended period of time). However, the logic that's looking at the mousewheel events and asking if a modifier key is held down is actually examining the *current* state of the modifier key rather than the state of the modifier key at the time that the mousewheel event actually occurred. Thus Firefox thinks that I'm holding down ctrl while using the mousewheel, rather than the reality where i used the mousewheel (by swiping) and then pressed ctrl-tab. Again, that's just a hackerly educated guess of sorts, I could be totally wrong.