As you may know, Firefox 39 should have been released till now, but this time it got delayed with a few days by Mozilla, because they discovered an important stability problem.
The official announcement (hacks.mozilla.org):
“Note: Firefox 39 has been delayed due to a last-minute stability issue. It will be released later this week. We’ll update this post when the release occurs. Stay tuned!”
Main features of Firefox 39:
Firefox 39 received an URL sharing features on social networks via the Firefox Hello, permitting the users to easily share links on Facebook, Twitter or LinkedIn, for example. Mozilla calls its Firefox Hello “the first global communications system built directly into a browser”, because it permits the users to perform video and audio calls directly from the internet browsers, without needing to install plugins or extra software and without having to be logged in with any account, all the users that have WebRTC-based browsers being able to communicate one with another.
Also, Unicode 8.0 skin tone emoji support has been implemented, some HTML5 improvements have been added and enhanced support when falling back from IPv6 to IPv4 is now provided.