Version 27 is an Rapid Release Cycle (RRC). Mozilla provides about 6 weeks support in the Rapid Release Cycle.
It doesn’t appear to be a major release. You can now run more than one service at a time with Firefox SocialAPI, allowing you to receive notifications, chat and more from multiple integrated services. Transport Layer Security (TLS) protocol version 1.2 support is being added, and the Android version is getting a few more languages.
Bug fixes and other changes until 2014-02-04 can be found here: http://www.mozilla.org/en-US/firefox/27.0/releasenotes/
You can download FF 27 RRC from here: http://www.mozilla.org/en-US/firefox/all/
Mozilla Firefox 27 RRC has been successfully tested with NetWeaver versions 740,731, 730, 711,702, 701,700 on Win 7 64bit, Win 7 32bit, Win 8 64 bit(desktop), Win 8 32 bit(desktop), Win XP, Mac and Linux.
As usual, for further details and SAP restrictions see: