Firefox 3 comes with several preferences baked into its options dialogs, but there are still a few you can only access by rolling up your sleeves and digging into its configuration manually. Power users have been diving under Firefox's hood to get their browser to behave just how they like since version 0.9, but Firefox 3 offers some new settings that customize its new features. Let's take a look at our favorite Firefox 3 about:config tweaks for customizing your browser.
What the heck is about:config? Firefox keeps its advanced settings in a giant configuration file in your Firefox directory, and even offers an advanced interface to edit that file in the browser itself. To make these changes, type about:config in Firefox's address bar. You'll get a half-joking, half-serious message about voiding Firefox's warranty if you change any settings. Press the "I'll be careful. I promise!" button (because you will be) and you'll be on your way. Warning: Keep track of what settings you change where in about:config, because one false move can make your browser go loony. You'd do well to back up your Firefox profile first before proceeding.
Got all that? Onto the tweaks.
Set Firefox 3 to use Gmail as your default mailto: link client. When you come across a clickable email address on web page, you don't have to copy the address, switch to Gmail, hit Compose on a new message, and paste it into the To: box. Firefox 3 can now register web applications like Gmail to handle certain link types. This trick isn't exclusively an about:config tweak—it involves some Javascript as well—but in the end you'll be able to click an email link and automatically launch a new Gmail message. Here's how to set Firefox 3 to launch Gmail for mailto links.
See richer image colors by enabling color profiling support. Firefox 3 can support advanced color profiles in digital photos, but ships with the feature turned off by default because it can cause a performance hit. If you've got a fast machine, and view digital photos online that look washed out because they're using a non-sRGB profile, you can set gfx.color_management.enabled equal to true to see richer colors. Here's more on this (somewhat controversial) color management tweak.
Tweak the AwesomeBar's suggestion algorithm. You've been living with Firefox 3's smart location bar (aka "AwesomeBar") for over two months now. Does it make the right suggestions for you? If you want to rank your bookmarks higher than your history—or vice versa—here's how to tweak about:config values to customize the AwesomeBar's suggestions algorithm.
Adjust the Smart Location Bar's number of suggestions. Speaking of the "AwesomeBar," if you wish the suggestion drop-down contained just a few more or less options, in about:config, enter browser.urlbar.maxRichResults in the Filter field to set this preference.
Make your bookmarks available to Launchy and Quicksilver. In the upgrade from Firefox 2 to Firefox 3, keyboard launcher maniacs may have noticed that their Firefox bookmarks didn't show up in Launchy or Quicksilver options on search. That's because Firefox 3 stores its bookmarks differently than Firefox 2 did. Here's the configuration setting that will make Firefox 3's bookmarks available to Launchy and Quicksilver.
Increase Firefox 3's popup count. Even though you told Firefox 3 to allow pop-ups from a particular domain (like Google Reader), it maxes out after 25. If you're sick of Firefox limiting your pop-up count to 20, adjust the dom.popup_maximum key about:config value to something higher (like 2000).
Change the URL bar's behavior. When you click on Firefox 3's address bar, the browser automatically selects the entire URL there. If you'd rather your mouse pointer just appear where you clicked, set browser.urlbar.clickSelectsAll to false in about:config.
Oldies But Goodies
While you're in about:config anyway, might as well set a couple of our favorite non-Firefox 3 preferences, too.
Disable blinking text. When the blink tag's got you down, you can save yourself from seizure and suppress blinking text forever.
Enable spell-checking in text fields. Firefox can spell-check as you type, and does by default in text areas, but not one-line text fields. In
about:config, set layout.spellcheckDefault value equal to 2 to enable spell-checking in single line input fields as well as text areas.Skip the add-on installation delay. When you're installing extensions left and right (and you know what you're doing), you don't want to wait for Firefox's built-in four-second countdown to complete before the Install button gets enabled. Here's how to skip the installation delay for Firefox extensions.
Get a Better about:config Interface
Finally, if digging around in Firefox's configuration area ain't your cup of tea, install the previously mentioned Configuration Mania extension, which puts a pretty interface on the most commonly-tweaked configuration settings.
What are your favorite Firefox about:config tweaks? Shout 'em out in the comments.