At the end of 2007, the now Mozilla Chief Executive Officer, John Lilly, estimated the install base of Firefox at approximately 125 million users. At that time, Lilly revealed that with Firefox 2.0, launched at the same time as Internet Explorer 7, the open source browser had virtually doubled its market share. And the fact of the matter is that throughout 2007, IE7 has struggled to go past IE6, and barely succeeded doing so at the end of the past year. Firefox 2.0 on the other hand, also benefiting from the end of support for Firefox 1.5, had no problems overtaking its predecessor.

"One of the most interesting things about Mozilla is figuring out how we're doing, and where to focus and spend time. We look at many indicators; some of the most important are things like the health of addons.mozilla.org, the volume and quality of community contributions to our platform and products, and the vitality of Mozilla-related discussions in the blogosphere. 2 other more numerical indicators that we track are Firefox market share (sliced a number of different ways) and the raw number of users of Firefox," Lilly stated at the time.

One of the most relevant aspects of the face-off between Internet Explorer and Firefox is the extensive customization permitted by the open source browser, as well as the community of developers that are using it as a platform. By contrast, IE is more inflexible due to Microsoft concerns related to support. Microsoft, unlike Mozilla, cannot afford to open up IE as a platform for add-ons. And add-ons represent a factor that will be increasingly beneficial to Firefox in the long run.

"addons.mozilla.org (AMO) recently hit a few milestones, so I thought an update (or perhaps initial view) of the add-ons community was in order. Earlier this week, AMO served its 600 millionth add-on download. That's original downloads, not including updates. We currently have over 4000 add-ons hosted on the site and between 800,000 and 1 million downloads every day. The site has around 4.5 million pageviews per day, not including services hosted on AMO such as update checks and blocklisting," revealed a member of the Mozilla team via the Blog of Metrics.

Mozilla estimates that over 100 million of the downloaded add-ons are still installed because of the add-on update pings volume it is receiving every day. 93% of the 100 million add-ons still installed are focused on Firefox 2.0 with 1% installed in Firefox 3.0 Beta. It would be interesting to see the add-on numbers of Internet Explorer...