Developer edition is a beta (or alpha since it derived from aurora line which came from alpha). You can say it doesn't have bugs but it has more than release editions. In my experience many more. Using a beta as a daily driver is not something to recommend.

Now, some distros like Debian have enough political power to get Mozilla to allow them to put Firefox branding on their altered user-freedoms-respecting repo editions of FF release. But most don't. So the only way to use actual release FF is to go outside your repos and use the unbranded version. Possible, of course, but tedious.

That is basically the whole purpose of that. A kill switch used when everything is on fire. Allows them to deactivate wide spread malwares when they discovered it. Although I have no idea whether it works or it is ever being used.

On the other side. The chrome store starts to behave badly and ban extensions they don't like for random reason after they implement that.

About mozilla, i don't know. will they eventually be like that, or they won't?