Dumping odd stuff that's not clearly from Mozilla and is poorly explained, without warning, is a fast road to lost trust.
I'm using Firefox 57 heavily (typing this in it), and actually really like it for a change. This after years and years and years and years of wanting to like Firefox but finding it completely and absolutely unusable due to performance issues.
(Chrome has been ... faster, but insanely aggravating in all sorts of ways, including utter and complete contempt from Google and the Chrome devs for users. The frustrations are rapidly mounting.)
Mozilla have just cost themselves some portion of their advanced user test base through abuse of trust. I really wish they'd not do that.