I've already seen a bunch of posts mourn the whole bunch of addons that will stop working end of this year. Probably, I'll lose some myself.
But personally, I trust Mozilla to do the right thing here. They've probably weighed the pros and cons, and made their decision. I'll see what the end result is. There's enough browsers to choose from nowadays.
Firefox has some unique things why I use it, first and foremost "search in links". Try it, tap the single-quote key and type text that appears in a link. Then hit enter. It's the fastest way to surf the web without a mouse.
But if end of this year comes and it turns out they screwed it up, fine -- I'll go and use another browser.