in a terminal will install any software available in the Fedora repositories (i.e. most unencumbered free open-source software, such as Firefox as you've discovered). The "Add/Remove Software" application does the same thing in a graphical way, or you can install "yumex" for a more technical graphical interface. For some more legally challenging software (e.g. codecs), add the RPM Fusion repos: http://rpmfusion.org/Configuration