Firefox 18 is expected to be officially released anytime now. However, as always, it has been uploaded to the FTP servers well in advance. If you wish to grab the stable release of Firefox 18 ahead of its announcement, scroll down and head over to Mozilla’s servers.
There are quite a few goodies for developers also in Firefox 18, including preliminary support for WebRTC and CSS Flexible boxes. Both of these features are disabled by default, and must be enabled from about:config. Other enhancements include support for W3C touch events, better image scaling algorithm, and support for retina displays.