For me personally, Privacy Badger and uBlock Origin are already there. I don't think I need a third one at all.
You seem to be more confident on their reestablishment of the extension ecosystem but didn't explain how you arrived at that conclusion.
But that's not what they do. Instead we do have a clear announcement on a feature removal and a vague hint that they might add it again in the future.
It's absolutely not sure that disabling non-store extensions is only a temporary defect.
If you have evidence that suggests otherwise, feel free to add it.
It does not help that their marketing language feels designed to consistently avoid any meaning whatsoever.
The update is going ahead because the new Firefox for Android is such a dramatic improvement along all other axes, and because, from a development perspective, the incarnation it's replacing is saddled with legacy and technical debt. It never received most of the benefits from Quantum, for example.
...and even the extension axis, from a power-aware Mozilla position. That's what makes it suspicious in the first place.
A few years ago they had a bug that added seconds to every page load that they didn't fix for half a year, but once an update coincidentally consolidates power at Mozilla it needs to be pushed for all its supposed benefits and despite all its known drawbacks asap.
We wouldn't buy that if it were Google or Microsoft and we shouldn't buy it in Mozillas case either. ... If they even announced that they plan to reopen the extension system, which they (to my knowledge) did not.
Personally I don't notice any grave difference between Firefox and preview. Apparently scrolling should be different, but my mid-range phone scrolls just fine in both apps.
An ecosystem where all extensions need to be channelled through one central power broker is pretty much the main requirement to allow them to do what Google is doing in the linked Pushbullet case.
edit: this is all factual, sadly downvotes won't change it.