Ok let see if you have "tar" installed go to the command line and type
you shold get somethung like
tar: You must specify one of the `-Acdtrux' options
Try `tar --help' or `tar --usage' for more information.
If so then go to the on the command line type
tar -xjf /path/where/you/downloaded/firefox-3.0.7.tar
or what ever the full file name is.
To start Firefox, run the firefox script in the firefox folder.
Firefox should now start. You can then create an icon on your desktop to run this command.
This is where I got the info