Hit Bug in Firefox and Flash
Here's an interesting problem that I ran into. I had a Flash movie sitting in an absolutely positioned div. In testing, there were times where a portion of the Flash movie was sitting too high and was actually positioned partly off the page. In this situation, the "live" area to click on a button within the Flash movie had shifted by the amount that the movie was offset. In other words, if the Flash movie was off the top of the screen by 20 pixels then I would have to position my mouse 20 pixels below the button in order to click on it.
The other interesting issue with this is that once you scroll down and scroll back, the hit area had corrected itself. The only solution was to make sure that no portion of the Flash movie ever appeared off the page.