EDIT: Apologies. Updated with a link to what gorhill REALLY said:
Manifest v2 uBO will not be automatically replaced by Manifest v3 uBOL[ight]. uBOL is too different from uBO for it to silently replace uBO – you will have to explicitly make a choice as to which extension should replace uBO according to your own prerogatives.
Ultimately whether uBOL is an acceptable alternative to uBO is up to you, it’s not a choice that will be made for you.
Will development of uBO continue? Yes, there are other browsers which are not deprecating Manifest v2, e.g. Firefox.
I’ve been using Chromium because it has excellent profiles support built-in. Firefox’s profile separation works via a plugin and is just awkward, unless something has improved recently.
Multi-account containers?
Those don’t exactly do what I want – which is clear separation of different work accounts. I’m not sure if this is what I need though, so perhaps I should take another look at what you suggested.
In firefox, type “about:profiles” in the search bar and press enter. (Please note that this shouldnt open your search engine) This will open a menu in that tab that claims: “This page helps you to manage your profiles. Each profile is a separate world which contains separate history, bookmarks, settings and add-ons.” I hope this is close enough to the solution youre after!