Firefox because it's plugins make mobile browsing bareable. I have a folding phone so I wish that Firefox would hurry up and copy Chrome's multi window feature, and then it would be the perfect browser for me.
I use Firefox on desktop too, but I've been experimenting with Arc the last few weeks to see what the fuss is about.
There's also Zen browser that's Arc-like and based on Firefox instead of Chromium. Zen lets you sync tabs with Firefox elsewhere (including mobile Firefox), run the full uBlock Origin, and it is a fully open source browser.
Sorry, I missed this comment until now. Thanks for the tip, I'll check Zen out.
The multi window feature I mentioned in Chrome is for foldable phones. Chrome allows you to open two separate instances and have them on either side of your screen; much like you can do on a desktop. I love the multi tasking aspect foldable phones allow, but very few apps allow you to have two instances of them running like that.