Some friends on Discord say that Opera could be better and, hell, some don't understand why I use Mozilla Firefox to begin with outside of privacy concerns.

Your friends on fed-cord are right. Why would someone use a free program over a proprietary one that clearly has more technical merit and advantages? Just use the right tool for the job (of surfing the Internet for hours each day since today's society demands that you do). Like come on, you don't even have to pay for Opera like how could it possibly be harmful? It's even owned by a Chinese company so hexbear will definitely approve.

Jokes aside: Your friends have no idea what they're talking about. We don't choose Firefox (and libre web browsers) because they are "better" but because they respect your software freedoms. We especially don't do it for "privacy" concerns since Firefox has telemetry, advertising and google search on by default.

Keep using Firefox, if you are concerned about privacy you can look at librewolf (or hardening Firefox). If you need a Chromium engine browser then use Ungoogled Chromium. Shits not complicated.