A new Firefox 4 Beta is out, and users looking to update may have noticed that the “Check for Updates” menu item no longer there. That’s because the Firefox updater has been moved to the About Firefox window.
To check for updates in Firefox 4, open the Firefox menu (or Help menu if you have the menu bar enabled), and click on About Firefox.
The About Firefox window will open and Firefox will automatically check for an update. If there is one available, Firefox will automatically download it.
When the download is finished, just click on Apply Update.