Advanced Firefox Configuration

I've used about:config to change the tabbed browsing configuration before someone came out with the tabbrowser preferences extension, back in 0.9 or so. Very handy to know. It exists in Thunderbird too, it's hidden in the regular preferences, under Edit > Preferences (Tools > Options, Windows lusers), Advanced, Config Editor button.

And there are some other tweaks you can make, like reverting back from the Awesomebar in FF3, or fixing some compatibility or speed issues. Here's 21 such hacks.