I don’t think Firefox will get into complete built-in ad blocking, like Brave does. But the days (or years) of uBlock Origin seem to be numbered because of the approach proposed by Chrome (called Manifest V3) to prevent extensions from modifying network requests, and being limited to just providing a block list of URLs for the browser engine to block (this design has been the case with Safari’s built-in content blocking).

I guess it boils down to your goal with using uBlock Origin. Are you anti-tracking or anti-ad? This blocks some ads as almost a side-effect but that isn't its goal. If ads aren't tracking, they're fully visible/working.

I use this because I value my privacy, but choose not to use uBlock Origin because I understand websites I use need revenue. It is about finding your own personal balance.

Don't, ever. There's no reason to trust Mozilla will keep this up forever. They're not even close to doing what uBO does. Blockers are best kept as a third-party solution with no conflict of interest. If too many people stop using uBO because the FF built in tools are "good enough", eventually we'll loose proper extension support and we will be at the mercy of browser vendors again.

I would switch to uMatrix (more detailed than ublock origin, by the same folks) where you can clearly see what sites are referenced and what kinds of things they are doing.

uBO relies on 3rd-party filter lists to know what to block. The most popular of these is Easylist, which is not well-maintained and doesn't have a good appeal process. I don't think Firefox should build this in unless they're going to support the maintenance of a high-quality filter list with a transparent add/remove process.