The “about:” URI schema has been around since the days of Netscape, but there is more to it than the common “about:blank” reference for an empty page. Some of these options give you an advanced view over Firefox and its cache – and others a just a bit of entertainment.
Here is a list of some common examples, all of these work in Firefox (tested in Firefox 3.6.3).
To use any of these, simply type them into the address bar.
about:
General information about Firefox (version, copyright, license)
about:blank
A blank page
about:cache
Detailed information about the contents, size and location of the memory, disk and offline caches.
about:config
Detailed lists of configuration options, including many that aren’t available in the settings pages.
about:license
Details of the license.
about:logo
The Firefox logo.
about:mozilla
An enigmatic quote.
about:plugins
A list of plugins with their MIME type, version and state.