enter the following text in the address bar:
about: shows info on Firefox version number, copyright, etc.;
about:config reveals the Configuration Console, a repository brimming over with scores of customizable settings;
about:cache displays a summary of both your memory and file cache, with a link to full file listings;
about:buildconfig lists the compiler options that were used to create your version of Firefox (and, since it’s open source, anyone can compile a customized version);
about:plugins enumerates your installed add-ons, which can be quite numerous since Firefox is designed to be modular and extensible; and
about:credits is an “Easter egg” that includes the names of hundreds of developers and testers who worked on the product.