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.
Man, you never worked for a large corporation that that had internal web based apps that only work on Internet Explorer and refused to update it.
I worked somewhere like that back in the 2008-2010 time frame. Thankfully, there was a extension, I believe the name was “IETab”, that would spawn a new tab in Trident (IE’s browser engine). So you could set certain sites to launch in one of those tabs and everything else would use standard Firefox. None of the people I supported were any the wiser. They just thought everything worked in Firefox.
Granted it was only that seamless because Windows already had that rendering engine built in. There are some extensions that do something similar with Chrome, but because of more modern security standards and whatnot you have to install extension helper applications which is gross.