Vimperator is not possible in the new Web Extensions, it requires customizing the UI in a way that Web Extensions doesn't allow. I am supremely salty about this still.

How about the power to customize every goddamn aspect of the UI? The power to make my browser behave the way I want it to behave? This is what made Firefox worth the while for thirteen, fourteen years or however long it's been. I really have no idea where to go from here.

As far as I know TreeStyleTab will still not be compatiable and it getting resistance on enabling the API needed to make it work like it does today.

It will end up being a far cry from what we have today and more like the Ridiclous and unusable "SideTree" menus that are available in chrome.

No TreeStyle Tabs, no FF for me. that is non-optional. I will switch full time to vivalidi that has a less feature complete vertical tabs built in.

There are also many other Addons I use today that look like their are going to be discontinued post FF 57 for API or other reasons.