We have indeed seen a severe dumbing-down of all of the major desktop browsers over the past few years, as mobile devices have become more widely used. So I think that what you're saying is happening, and will continue to happen.

Desktop browser users should not have to suffer because mobile users choose to use platforms that are crippled in so many ways. Nor should desktop browser users have to install numerous extensions just to bring modern desktop browsers back to the level of usability we had a few years earlier. Yet with each new release of the major desktop browsers, we find ourselves in the position of reduced functionality, and the need for more and more extensions to restore the now-missing functionality.

They are doing a major UI overhaul - the design itself is unstable. So there are valid reasons for current visual add-ons not working - the majority of bugs reported by users would be caused by plugins designed for a different user interface, making it useless as feedback. That would defeat the purpose of having an open beta. Meanwhile the plugins should not yet update because the interface can change any update. So for now it's a chicken/egg problem but I'm sure that once the interface stabilises things will be as they used to.

So while it is good to stay on your toes, I don't think you realistically have to worry about this going to be a permanent issue.

NoScript is unavailable because current NoScript only works with the classic 'everything in one process' Gecko model & associated plugin model.

Firefox for Android isolates content into multiple processes (this is literally a requirement on Android due to their horrible memory management), which means plugins written in that fashion simply can't work. Unfortunately, at present this excludes NoScript. It's possible it could be fixed, though; I'm not sure.