Firefox 3.6—the latest version of the popular open source Web browser—was officially released in January, but there are still many users who have not yet updated. In an effort to increase awareness about the availability of version 3.6, Mozilla announced today that it will start rolling out upgrade notifications to its users through the browser's built-in update system.

According to Mozilla's statistics, the new version has already been downloaded over 100 million times since its release in January. That doesn't include the significant number of existing users who have already migrated to 3.6 by using the browser's built-in upgrade system without being prompted to do so.

Firefox is arguably one of the most successful open source software projects. Mozilla celebrated last year when Firefox surpassed 1 billion total downloads. The current number of active daily users is said to be over 350 million.

Getting such a large user base to migrate to the latest version is not an easy task, but Mozilla always manages to get the job done. Studies show that Firefox ranks high in update effectiveness, getting over 85 percent of its users to switch to a new version within 21 days after release. The only browser that has a better upgrade penetration rate is Chrome, due to its highly aggressive background updater.

Firefox 3.6 is a somewhat modest incremental update. It brought several noteworthy new features for users, such as the Personas lightweight theming system. It also offers some compelling new capabilities for Web development, including CSS gradients, client-side filesystem APIs, and the @font-face feature.

For more details about the automated upgrade process, you can refer to the announcement in the Mozilla Developer Center.