It used to be webkit, but it was rebased on Firefox and uses Gecko now.

The problem for me is that I’ll keep things open for reference. Like I might have a few tabs open with info about a game I’m playing, or researching a purchase I’m trying to make. So having those grouped on mobile is super helpful.

I’m glad they’ve added it to desktop, but based on my usage it’s more important for me on mobile. Hopefully they bring it to Android soon.