I think we're more at the point where they should be getting arrested by local cops. It says a lot that local cops are defending them instead.
Saying "I will shoot you" is illegal, no matter who you are. It doesn't matter if they work for ICE, the FBI, the local police, or McDonalds; they should be arrested if they say that.
How do I prevent new antifeatures from being added? How do I even know about the new antifeatures as they are added? Does Mozilla publish an RSS feed of each antifeature like this that they add, that gives a quick explanation of how to undo it?