Faster page loads are on the way, as is heightened browsing security.
Windows users will no longer need to give permission each time a browser update arrives.
Mozilla this week began blocking outdated versions of a Java plug-in in Firefox for some Mac users.
Instead of having tabs at the top of the screen, Metro-style Firefox may use a sidebar, with thumbnail images for each tab.
Next month's Firefox 12 will be the last version of Mozilla's browser to run on early editions of Windows XP and the 12-year-old Windows 2000.
At some point during March, Google lifted the penalty it had imposed on Chrome the first week of January, when it demoted the search ranking of the browser's download page.
Mozilla is currently testing default encrypted Google searches for all Firefox users, with the intent to make all Google searches encrypted in the near future.
Mozilla hailed features added this year such as add-on compatibility and synchronization improvements, silent updates and better organization of development tools.