FF4 does not display animated GIFs correctly, especially rollover repeats. FF4 will ignore stylesheet commands, such as font settings, table cell spacing and borders. FF4 will frequently freeze on opening, or display even simple pages very slowly. FF4 "Page Info" box (Media section) will not display most of the associated images. I have been forced to uninstall FF4, and go back to FF3.011, which had none of these faults. In my opinion, FF4 has been improved to the point where it no longer works.