To extract the tar.gz file go to a terminal and cd to the directory containing the file and type tar -xzvf firefox-1.0.4.installer.tar.gz. Then type
cd firefox-installer, then ./firefox-installer.
Or if your using KDE you can just right click on the file go to extract and click extract here. Then move into the firefox-installer directory. Right Click on empty space go to action and open terminal here. Then type ./firefox-installer at the terminal.