The second 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 2 can be downloaded and run, without having to install anything.
The Mozilla developers haven't made any formal announcement regarding the second Beta, but they do offer some details about the general improvements that will make their way into this particular branch.
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.