Quoting acohen36@sdf.org (acohen36@sdf.org):
From what I'm seeing now, and FWIW, both the 64-bit open source Brave* browser and the 32-bit open source Palemoon browser will _still_ be supporting many of our most important browser extensions into the near future.
As will Firefox-ESR, SeaMonkey, and Waterfox.
*An interesting fact to note about Brave is that their Mission District HQ is ~3/4 hr MUNI busride from Mozilla's SF offence [9] ear Rincon Point.
Comments from announcement-forwarder Michael P, from Rick M, and from others are expected and of course welcome :-)
I'm backlogged on correspondence, and also jetlagged, having just gotten back from a couple of weeks in Helsinki and Stockholm, so don't hold your breath waiting for me to address this.
Moreover, it's already been extensively discussed elsewhere: http://linuxmafia.com/pipermail/conspire/2017-February/008707.html http://lists.svlug.org/archives/svlug/2017-February/062344.html https://lists.dyne.org/lurker/message/20170223.160150.c29d18d7.fi.html (See threads beginning at those links.)
The dropping of XUL & XDL (extension interface) from the main Mozilla codebase (after verion 56) creates unfortunate short- and medium-term consequences, though as mentioned there are indeed technical reasons for it. But there will be some very serious permanent loss of functionality, make no mistake: There is simply a great deal that WebExtensions cannot do and probably will never be able to do, things classed as 'chrome' alterations, hence involving XUL & XDL.
The recent dropping of ALSA sound support is even more regrettable IMO: I continue to regard PulseAudio as something of a horror, though one can substitute apulse as a crutch for applications that expect PulseAudio.
Last, what I've seen about code-signing has been so far troubling, with Mozilla's builds reportedly _not_ giving users control of the keychain. Of course, this being open source, anyone sufficiently motivated can maintain a patchset to restore that control. (There may have been newer developments in this area, and I would not necessarily have heard of them.)
Also, as Akkana noted on the SVLUG discussion, Firefox-ESR will preserve the ability to switch off mandatory enforcement of extension signing, via an about:config toggle (that in Mozilla's releases will be switched on by default).
So, it's the usual sort of thing where less-technical users are going to get steamrolled.