Firefox users who cannot wait to update the stable channel of the web browser from version 10 to 11, can download the new version from the official Mozilla ftp server or third party download sites early. Please note that while it is unlikely that the final version will get replaced in last minute, it has happened in the past. It is recommended to wait for the official release announcement if Firefox is running in a productive environment, or if you do not need to have access to the new feature set introduced in the browser right away.
It will take approximately three days before the internal updater picks up the new version and offers to upgrade the browser automatically. You can check for the installed version with a click on Firefox > Help > About Firefox.
The beta release notes highlight the changes that Mozilla has implemented in the new version of the browser. Probably the biggest feature for end-users is support for add-on synchronization as part of Firefox Sync. This feature can be used to synchronize installed browser add-ons between all versions of the browser where sync is enabled on.
Firefox users who are using Google Chrome as well on the system can now migrate their bookmarks, history and cookies from the browser as part of the migration process.
The majority of features are only interesting for web developers and developers in general. Firefox 11 supports the CSS text-size-adjust property, and the outerHTML property. Developers can furthermore make use of the Style Editor for editing CSS, and the new Page Inspector 3D View which is available if the computer is compatible with WebGL.
Firefox 11 furthermore supports the SPDY protocol for faster page loads, and XMLHttpRequest HTML parsing.
The change log lists unresolved issues, among them some that have been noticed by some users in previous versions of the browser as well. This includes the slow scrolling in the Gmail window, or jerky scrolling and text input under certain conditions.
It is not really necessary to update the browser right now, instead of waiting the three days before the official announcement is being made. It would be different if stability or security updates were included in the release.
Update: Mozilla is preparing to replace the current version with an update. It is not advised to download the release version just yet.