If you can can tell us what problems you had with firefox, I will see if I can help. Release 1.5 was not a clean product. However, release 1.5.0.1 just came out. There are a lot of bugs fixed in this version.
As for installation/uninstallation, keep in mind, we are talking about OS X. In a BSD/Linux/Unix system, firefox can be put anywhere. Unistallation? Delete the directory and clear ~/.mozilla. That's it. There's no registry joke here.
MPlayer plugin can almost handle any type of multimedia files, even if it's a .rm or .rmvb file.