Here are all of the useful (and not so useful, but still funny) about: triggers you can type into your address bar.
about: — The same page as “Help -> About”.
about:blank — A blank page. Useful for setting as your homepage.
about:cache — Displays cache statistics and disk cache directory location.

about:config — GUI for modifying user preferences.
about:crashes — List of Breakpad crash reports, with links and datestamps. Only in products based on Gecko 1.9 or later (Firefox 3, Thunderbird 3, SeaMonkey 2).

about:credits [...]

Are you one of those people that likes to tweak around with what is behind the pretty Firefox curtain? If you want to jerk back the interface and get to the guts of the browser, you might need to jump here or jump there to get to the settings you need.
One person made this job a little easier with the Edit Config Files extension for Firefox. Once installed it gives you quick and easy access to such things [...]

The folks over at Lifehacker have put out a nice article about the extension for Firefox known as About This Site. They cover this little beauty from head to toe and let you know why you may or may not be interested in using it.
When you happen upon a new web site – or you’re just interested in finding more about one you frequent all the time – it’s difficult to get a sense of how popular it is, [...]

I ran across this link via one of those bookmark tracking services. For those of you who might not know about all the hidden configuration pages you can access via Firefox, this would be a nice place to start.
I found myself staring at the “about:blank” parameter for an IE installation today, and that got me thinking if it works in other browsers too. It did. I’m using Firefox, and that cleared the address bar to a blank. And then [...]