The first beta release in the new Firefox 23.x branch has been made available for download, by Mozilla, for all available platforms.
The binaries for Mozilla Firefox 23.0 Beta 1 can be downloaded and run, without having to install anything.
There aren't too many details about the changes and improvements in this latest version of Firefox, and Mozilla hasn't bothered to update its website with the information about the release.
A detailed list of upcoming features can be found on the official website.
Remember that this is a development version and it should NOT be installed on production machines. It is intended for testing purposes only.