Mozilla add-on ninja Justin Scott has revealed that Firefox and Thunderbird users have downloaded over 600 million addons from the addons.mozilla.org (AMO) web site. Scott also notes that AMO receives over 100 million addon update pings every single day, a statistic that provides some insight into the total number of addon users. AMO hosts over 4,000 individual addons and facilitates between 800,000 and 1 million addon downloads every day. The site itself gets about 4.5 million daily page views.

Support for addons is often cited as one of the most compelling features of the Firefox browser. The inherent flexibility of Firefox's XUL user interface system provides addon developers with a lot of power and extensive control over the manner in which the program operates. This has led to a rich ecosystem of useful third-party addons that offer a wide range of specialized features. Although addons add a lot of value to Firefox, they are also a liability in some ways because, for instance, conflicting addons can create performance and stability problems that are difficult to troubleshoot.

Mozilla also published a breakdown of the update ping information by version, revealing that 93 percent of all update pings come from Firefox 2 users, 2 percent come from Firefox 1 users, 1 percent come from Firefox 3 users, and 4 percent are from Thunderbird users. In another recent blog entry, Scott notes that the Rock Your Firefox app for Facebook, which allows users to share their favorite Firefox customizations with friends, has over 4,400 current users.