He reviews some new and updated features plus some how-tos to change them.
Linux users: Unless you installed it manually it will be updated through your distro.
"Mozilla will upgrade the stable channel of its desktop browser to Firefox 20.0 today. The front page at the time of writing is still linking to a download of version 19.0.2, but you can use this link to download the new version of the browser right away. Make sure you change its url if you need a different localized version, this one downloads the US version of Firefox.
"You also find the download on Mozilla's official ftp server. Later today, Mozilla will start distributing Firefox 20 via the browser's automatic update feature, and you can download it from the official website then at that time as well."
Source: Ghacks Technology Newsletter
Firefox 20.0: Find out what is new
Go get it.