Opera had its own browser engine (Presto) and had a native UI (or if it wasn’t, it felt like it because it was really snappy). I think for some period they use

Opera had its own browser engine (Presto) and had a native UI (or if it wasn’t, it felt like it because it was really snappy). I think for some period they used Qt on some platforms. But early Opera was really a fast and innovative browser. Opera was one of the first (if not the first) browser with tabs and popup blocking. Opera Software even owned Fastmail for a few years (until an employee buyout). It's sad that they have gone down the drain.