Nothing wrong with Opera. It’s based on Chromium, which means it’s based on the same engine as Chrome and Edge. It has a built-in VPN function; so, you can have that sort of privacy protection built in to your web browsing, depending on your trust for the company behind Opera (also called Opera). They have been involved in some questionable dealing in the past; but, there is no evidence that they are harvesting data with the VPN. The tl;dr is that it’s another way to have Chrome without directly using Google Chrome.
As for FireFox. It’s a great browser, I use it myself. It’s based on it’s own engine, Gecko. The Mozilla Foundation seems to care more about privacy and web standards than any other browser author. Though, this has pros and cons. On the plus side, FireFox can be configured to be very privacy preserving and some extensions (e.g. UBlock Origin) tend to be better at privacy on FireFox than Chromium based browsers. That said, some websites will expect Chromium and may break on FireFox (though, this is often because of explicit by web site developers. User agent spoofing often shows that the problem is fictitious).