There are few places one can go where a gleaming pair of yellow arches cannot be found proudly declaring some variant of "Over 99 Billion Served." Now browser-maker Mozilla has something in common with McDonaldland: As of last week, Mozilla has officially served up their billionth add-on.

One of the big draws for Firefox — outside of being Open Source, of course — is the plethora of extensions, themes, and other tweaks available to make one's browsing life complete. Way back in 2005 — when Firefox 1.5 was still Deer Park Alpha — someone got the bright idea to start tracking the number of add-ons downloaded from Mozilla's servers. Now, three and a half years later, the tick marks have finally tallied up to one billion, placing Mozilla — and all the developers, testers, users, and everyone else involved — firmly in the one billion club.

The one billionth download — which, sadly, cannot be traced to a specific add-on — came just twenty-four hours after the launch of Mozilla's "Fashion Your Firefox" application, aimed at bringing the most popular and relevant extensions to users in an easy-to-understand point-and-click interface. The tool presents users with nine sets of extensions, categorized by common on-line activities like "News Junkie" and "Social Butterfly," with the intent of making it easier for users to find extensions that match their on-line activities without having to navigate the sometimes overwhelming selection available from the normal add-on repository. The list draws heavily from Mozilla's Recommended Add-Ons section, and has been specially vetted for user-friendliness, compatibility, and positive user reception.

Reaching a billion add-on downloads is just one among many recent achievements that demonstrate Firefox's increasing distribution. Just under a year ago, Mozilla released figures estimating over 125 million instances of Firefox running worldwide, while the June release of Firefox 3 set a world record for software downloads and brought Mozilla's servers to their knees. That, of course, all built up to the release of July's market share numbers, which showed Firefox breaking the 20% mark eight times, while the other browser saw some of its lowest numbers in recent memory.