Are you using FF3 on windows as well?
Yes. So now I don't know what to think (with regard to what Noel's using).
Forcing extensions to run regardless of their compatibility is a nice thing to be able to do, but it has its downsides. It seems to work fine without the !important directive on FF3 ubuntu 8.04 AND on my laptop in windows, but I'll need to reboot to be sure. I'm sure I needed it before, but it may have been a result of the way I was originally using the image.
Removing !important does indeed fix it. I'm not sure why this should be the case, since it was all legal CSS, but then no browser seems to fully support any CSS standard in the first place (even Firefox).