Neat! I'm not the grandparent poster, but I also can't stand horizontal tabs, probably because I'm a tab hoarder. But with screens wider than they are tall, vertical tabs make sense, and each new tab doesn't truncate all other tabs' titles.

I looked up MS Edge's implementation, it seems it only shows the tabs either on top or on the left of the window, with Vivaldi you can set it at any edge of the window, I have mine on the right side.