Along with Linux, FireFox is one of the most successful OSS projects.
Firefox is probably one of the most familiar names in OSS and the community of users is huge. You can run Firefox right now, quite easily, because it is available for all major operating sytems.
Firefox is a slim, fast web browser which is highly customizable with plugins and the look can be modified with themes. Many choose Firefox because it is less prone to many of the attacks targeted at Internet Explorer, or because it allows you to browse the web in a way that reflects your needs.
Firefox is more than an OSS success story, it is deeply reflective and connected to the entire movement. Netscape Navigator was once the dominant web browser until Microsoft focused on usurping their lead, basically by offering Internet Explorer for free. Users dropped the Netscape version and their market share fell. Then, in 1998 encouraged by the Cathedral and Bazaar, most of the code for Netscape was released to the open source community. The result of this was the Mozilla Foundation. Firefox is a branch of that project.
