I am using Firefox 3.0.10 on Mac OS X 10.5.7 and the resizing animation is extremely choppy. It works perfectly fine on Safari 4 Public Beta though.

Hi again.
I was disappointed when firefox 3 came out. It uses a new rendering engine. Firefox 2 animated just fine and firefox 3 went significantly backwards in that regard. This is especially true when it is animating over a page that contains iframes and, to a lesser extent, numerous images. In those circumstances it paints the overlayed floatbox in chunks, first the part overlaying the main page area and after that the parts overlaying the iframes and images. It can look quite crappy. However, the floatbox code can only tell firefox what to render, not how to render it. Like I say, I was disappointed.

The degree of choppiness is directly related to the size of the images being loaded. Avoid at all costs loading an oversized image and scaling it down to screen display size with width and height parameters. And if you're loading a natively large image and it's animation is too choppy for your tastes, you can always turn off zoomImageStart, liveImageResize, and any other animation options that aren't working well for you on your page.

Cheers...