CSS "position:fixed" rendering in FF 3.5 vs. 3.0

Is there a fundamental difference between how position:fixed; is handled by Firefox 3.0 and Firefox 3.5?

I ask this because I had been using Firefox 3 as the development platform for an ongoing project and this was upgr开发者_StackOverflow社区aded to Firefox 3.5 today.

The structure creating the trouble is a div situated at the very top of the viewport position:fixed; top:0; z-index:3

This div sits on top of a large image which may be scrolled down by the user.

Previously, with FF 3.0, the image used to scroll smoothly without affecting the top div. However, with FF 3.5, the top div flickers and oscillates about its supposed position as the image scrolls!

Does anybody know how to get the top div back to serenity?

According to this question on stackoverflow you can add overflow:auto to the element.