Well, I'm a Firefox user, not an extension developer, and I much prefer a performant browser with modern security features (and the ability to implement more in the future, which they couldn't do pre-57). I've lost a couple extensions during the move, but the tradeoff is well worth it to me.

And it sucks that you don't feel that way -- it really does -- but I suspect the vast majority of Firefox users feel as I do, and in the end Mozilla needs to cater to the most users possible.