While adblocking has gotten most of the focus, it isn't the only functionality that is being limited or made more complicated. One of my favorite extensions is still not available for MV3 because of complications: https://github.com/openstyles/stylus/issues/1430

Yes, hence "less of an issue," not "not an issue."

At least when I last tested, Vivaldi on Android's adblocking is pretty far behind uBlock Origin -- it doesn't get nearly as many anti-adblock interstitials as it should.

At this point, I wonder why Firefox doesn't have a vivaldi-like tracker and ad block interface.

Perhaps it has to do with being a Google-funded browser.

I wonder how hard that would be to implement for someone who knew how to do it? Or if the code for that in vivaldi is open source?

It does. Click the little shield in the address bar. I assume it blocks some ads even if it's not as effective as uBlock Origin.

It blocks trackers, which means ads usually get caught up in the net. It's anyone's guess if the ones that makes it through aren't tracking, or are successfully evading (I'd wager the latter).