Re: Any way to tell?
I will be sticking with Waterfox and/or Pale Moon. The dev of Waterfox has only committed to supporting the older addons "as long as possible," so it suggests that eventually it will be Pale Moon or nothing.
Pale Moon is better than FF in some ways; for example, it retains the classic, non-Australis UI. On the other hand, it has no E10s support, and it probably never will. The lack of smoothness and stuttering that causes will remain a part of PM as they have been part of FF for ages. It's still far better than accepting a neutered FF that looks like Chrome and won't accept addons to change it by a mile, but as long as I can have e10s AND my addons, that is the better solution right now, as I see it.
For the immediate future, Waterfox will be closer to what I am used to, but the question is for how long. "As long as possible" is vague and ambiguous; it could be "possible" by his estimation for a decade, or maybe only for six months. It also suggests a question of where these addons will be hosted after Mozilla's suicide bid; certainly, they're not going to keep hosting addons that no longer work with their "it's basically a skin for Chrome" version of Firefox.
I know one thing, though: Given a choice of using a FF derivative that cuts off most of my addons or an out of date, old version of FF/WF that still allows the addons (even if the addons themselves get dropped by their devs because of Mozilla's actions), I would take the latter. FF 57, like Windows 10, does not and will not exist, as far as I am concerned. It's not an option; the options consist of competing products or using older versions regardless of the security implications. It's not a place I wanted to be, but the choice was made for me.
You know, this always happens with software. I've come to realize that all software devs eventually will move to sabotage their own product in a fit of development suicide. Microsoft is doing that with Windows now just as much as Mozilla is doing it with Firefox. It already happened to Opera, and the wayside is littered with corpses of other once-relevant products that are no more.