Can/Do you want to comment on Mozilla's efforts to work with extension developers to bring everything needed to WebExtensions? While the promise sounds great, I would expect there are issues that make it not as easy in reality.
They are trying I guess, and may succeed for a bunch of use cases to bring what's required. But certainly not all. Even the add-ons that can be somewhat reasonably be ported will have to deal with limitations, and I think the quality of some of those ported add-ons will take a (major) hit.
To elaborate:
If you're doing "web stuff", toolbar buttons, and request stuff (adblocking etc), you'll probably be fine. If you're lucky enough that you only need a few additional new things and your name is e.g. Giorgio of NoScript, you also will be probably fine.
If your add-on does not have a sizable user base, and you do fancy things like modding the browser UI itself, or doing something else not entirely "webby", your outlook is a lot less rosy.
It's still not clear to me whether you actually tried to work with the Mozilla devs or if this is still fueled from your initial (in my opinion rather rushed) statement and some form of false pride.
But yeah, I'd just like to say that in case you did not do your best to maybe get to a solution with the Mozilla devs, that I'd appreciate it, if you could try again.
I don't personally use your add-on, but I know that a lot of people do and I think that this initial discourse to get some of the APIs sorted out is rather important.
Even if you don't end up writing the extension, it'd be good to have reasonable APIs at least drafted. So that maybe someone can offer a half-assed Down Them All, which maybe is already good enough for some people, and then maybe that add-on's developer can continue working with Mozilla to get a proper API fully sorted.
You should also consider that Mozilla started out with this "webby" state from Chrome. Anything modifying the UI and so on still needs to be defined. Once they have some of the other UI-APIs worked out, it'll be easier for Mozilla to fit new libraries into there and then it'll also be easier for Mozilla to work with your API needs.
I volunteered massive amounts of my time for mozilla for more than a decade now, not only developing. I do not consider my previous statement rushed, but a realistic prediction based in a decent foundation of experience and knowledge, and - rather unfortunately - so far I am right and there is no indication that that's about to change.
I'd really like to share your optimism here, but really, knowing what I know, I just cannot.