As part of Mozilla’s new rapid release development process the beta development channel has been updated with a Firefox release candidate. For detailed information about the changes please visit:

Firefox: http://www.mozilla.com/firefox/5.0beta/releasenotes/
Firefox mobile: http://www.mozilla.com/mobile/5.0beta/releasenotes/
For desktop users, if you previously installed a beta version of Firefox 4 you will receive an automated update notification within 24 to 48 hours. Mobile users will need to manually download Firefox Beta from the Android Market in order to join the beta development channel.

We highly encourage add-on developers to test their add-ons with the new version and mark them as compatible as soon as possible. The Mozilla Developer Network has detailed information about changes in the new version for add-on developers.

To manually download the latest pre-release software from the various development channels, please visit:

Firefox: http://www.mozilla.com/firefox/channel/
Firefox mobile: http://www.mozilla.com/m/firefox/channel/
As always, the latest released version of Firefox can be downloaded from http://firefox.com.