Apps Lost Due To Frequent Update Of Firefox

With the advent of Firefox 57+, does it mean that in future, all compatible add-ons/extensions will still be usable with all future versions of Firefox WITHOUT the developers of the add-ons/extensions having to update their apps?
If that is so, it will be a tremendous improvement as many extremely good apps were lost in the past due to developers getting fed-up with having to update their apps far too often!

As it is right now, I’m migrating a bit to SeaMonkey, which, for now, is compatible to most add-ons that are being left behind by Firefox. I’m getting tired of having good add-ons getting left in the dirt due to nearly weekly updates. What add-ons? Big ones are Greasemonkey, Save Images, Image Toolbar, VideoDownloadHelper, RedirectBypasser… all I can get in Seamonkey.