I just tried Firefox for the 5th time (over the past 2 years) last week and it was so much slower to load pages, and the scrolling experience was quite poor.
Samsung's dark mode is outstanding and while less flexible, a lot less clunkier than Firefox extensions. Any browser without a viable Dark mode setting (for sites i.e.) is a non-starter, especially when you can enjoy dark mode reading in bed with a great OLED screen.
Tab browsing and private mode both work really well.
Text zoom and general page layouts are much more readable. Accessing old.reddit.com via Firefox was a mess with the font being tiny, whereas it is totally usable on Samsung's browser.
Ad blocking works quite well as well. At the end of the day, Samsung's browser gets out of the way and executes really well on all the main things you'd want in a browser.
I really want to use Firefox or a similar browser that I trust more with my privacy, but at the moment, Samsung's browser is miles better than all the other browsers I've tried using.
For time being (fast ads free internet on android)
Kiwi browser https://kiwibrowser.com/
Ublock Origin https://github.com/gorhill/uBlock