Open the firefox folder and double-click on that cog-like icon labelled “firefox” to launch the web browser.
Then move that extracted folder to your user root directory i.e., /home/. Double click the tarball to extract it on your current directory. Once you’ve downloaded the Firefox tarball, it’s time to head over to the file manager (Nautilus) and browse to the Downloads folder. In case you are browsing from Iceweasel, you will get a prompt to download a *.tar.bz2 file (aka tarball file), first tick Save the file and select OK to start downloading.