Hello is an interesting service Mozilla has in Firefox that provides a WebRTC-based alternative to services like Skype. Mozilla has included it in Firefox for some versions but have now decided to drop the Hello addon from the upcoming Firefox 49. Version 49, which is expected to be released in September, will come without support for Hello. Support for the underlying WebRTC technology itself may remain intact.
After September 13, 2016, Firefox Hello will be removed from the stable branch of the browser. Note that beta and developer builds of Firefox already come without Hello.
Are you using Firefox Hello? Will you miss this feature?