Browsers still have a lot of memory usage on their own.

I am running Arch Linux here. When I boot my machine into a full desktop environment it uses 1.1 GB of memory total, for everything.

If I open Firefox, it in itself uses about 1.3 GB to have Firefox open with just HackerNews in 1 tab. I have no extensions except uBlock Origin.

And it’s the applications using web browsers as their UI kit that are the worst offenders in my experience.

I disagree, there is low-hanging fruit Firefox is leaving on the table. The main thing that comes to mind is tab unloading. They don't unload tabs automatically like chrome can.

I was pleasantly surprised at the tab unloading settings under "memory saver" in ungoogled-chromium.