Go with Vivaldi instead of Opera, for a number of reasons including privacy.
When I used Opera, I used an extension which allowed me to install regular extensions from the Chrome store, so that’s an option. But I switched away from it to Vivaldi and that allows you to just install Crome extensions directly.
I have a feeling it might use more memory than Opera though, but I have no real evidence of that.
I was a bit surprised when all my extensions suddenly stopped working last night, however other than that, I’m having mostly the opposite experience to you.
I’ve been mainly using Firefox for the past 5 weeks, and I’m finding it surprisingly good.
(For background, I used FF for years, but switched briefly to Chrome a few years back, then switched to Opera(Chrome) until last year when I wasn’t happy with some things and switched to Vivaldi.)
I’d been using Vivaldi on my old laptop because I’d tried various versions of FF over the past few years and they were just too slow or memory hogging. Vivaldi was nice, though used a fair bit of memory.
When I got my new laptop I installed the latest version of FF on it (for reasons I forget now), and planned to install Vivaldi at a later point… and just haven’t ever really needed to because FF works great. I don’t know if it’s the new version or the new PC, but it’s super smooth even with 3 windows and 75 tabs, and the UI seems to work really nicely for me, and because I use FF on Android (which is also great now, after a decade of being janky) and Pocket the integration with mobile is handy.
If I have 2 complaints about FF now, it’s (a) there is no way to make standalone desktop apps (which is annoying as FF was actually the first to demo that feature, back in the day), and (b) the number of extensions is dwarfed by Chrome, and a lot of them are relatively new/unused so it’s hard to know if they’re reliable. (oh, and © the user account switching isn’t great, but I rarely use that).
But the core browser works great for me.
AFAIK the certificate snafu should be fixed, so it’s annoying, but I’ll probably stick with FF and use Vivaldi as a backup for anything that needs Chrome.