Hasn't Firefox moved to the Blink engine that Chrome uses?
Opera has moved away from their custom built Presto engine and gone to Blink in versions 15 and up, too, and it has generated a lot of complaints from those who really like 12.
Among other things, bookmarks are gone or have been altered radically in a new thing called Stash, you have to relearn the browser, I've read, and mouse gestures have been reduced.
I'm really not very clear about all this because I'm sticking with version 12.17 (an update to 12.16 Opera made for stability and as a concession to us fossils, I suppose) but if Firefox is using Blink now, that may be the source of your disgruntlement.
(Fun word I seldom get to use.
)
Gil.