Download Firefox 18 with Faster Page Loading, Retina Support & Much More
Firefox 18 also implements basic support for WebRTC, which will eventually allow compatible browsers to perform certain high-end functions such as video and voice calls without the need for third-party plugins.
Apart from these features, there are some bug fixes and other smaller features. You can read full release notes from here Official Firefox 18 release note.
You can download Firefox 18 offline installer from the link below.