Firefox 40 Rapid Release Cycle (RRC) was released on August, 11th.
According to the release notes the browser now has support for Windows 10 and protection against unwanted software downloads.
It is available for download from http://www.mozilla.org/en-US/firefox/all/.
Mozilla Firefox 40 RRC has been successfully tested with NetWeaver versions 7.40 SP12, 7.31 SP17, 7.30 SP14, 7.11 SP13, 7.02 SP17, 7.00 SP30 on operating systems: Win 7 64-bit, Win 7 32-bit, Win 8 64-bit (desktop), Win 8 32-bit (desktop), Win 8.1 64-bit, Mac and Linux in the areas of NW – PLS, WD ABAP, WD Java, NWBC, ACF, BI, UI5, FPM , Web CUIF, EP, Adobe, Fiori – FLP on ABAP.
As usual, for further details and SAP restrictions see: SAP Product Availability Matrix (PAM): https://service.sap.com/sap/support/pam and Firefox browser note: https://service.sap.com/sap/support/notes/990034.