TL;DR
Don't use Opera. Opera is bad. Stay on Firefox.
I would not switch to Opera, or anything else simply because it's Chinese, the same reason I would't reccomend against for that reason. Opera is proprietary, meaning the source code is hidden, and it tracks activity by default, selling that info for a profit. Firefox is open source and run by an nonprofit (albeit one with strange financial decisions). It also tracks much less by default, with the potential for it to be completely removed by something like arkenfox. Speeds also don't matter as much as you may think, Firefox is fast enough, and the Unlock Origin extension can help with browser speed in some cases. If you really want something Opera provides, even Vivaldi is a better option (though I don't suggest it for similar reasons to Opera).