Having switched from Vivaldi back to Firefox about a year ago, the Vivaldi speed dial is similar to the pinned lists of favorites, but it's much more user friendly. You can customize how many sites you see, how many are in each column, number of columns, etc. You can also change the icon to be anything you like. It certainly wasn't a dealbreaker for me personally, and as you said, pinned favorites serve the same purpose, but it does feel more restrictive on FF.
It used to be more customisable but FF wanted to dictate what users saw, for some reason, partially advertising ("recommended by pocket"). They really like to imitate the worst of commercial enterprise sometimes.
It has become a little more customisable now, thankfully.
they don't let you run in browser contexts normally but they definitely let you set your own new tab page(with webextension privileges) as part of the extension which lets an extension do whatever they want.
Sounds kinda similar to what you are looking. It does No. of sites, custom columns, custom pictures, and custom backgrounds. It really gives you a lot of control compared to all the other extensions I tried.
It's way more than just pinning ! I organize my YouTube subscription in folders with themes like tutorials recipes and subfolders...you can do that on Firefox with the bookmark toolbar but in a less user friendly way and less visually pleasing way toi. what makes it worse is that it used to be possible on Firefox! It's not a deal breaker or anything ! But I miss that XD ! I had a hundreds of bookmarks organized on Vivaldi ! I still don't know how to "transition" that to firefox :/
