Please, Firefox, for the love of everything, add a good, easy, natively integrated, one-click-to-enable vertical tab list like Edge's. That's the only thing keeping me on Microsoft Edge and it's a dealbreaker for me. The extensions that add ones are just not as good.
Vertical tabs are The Reason why I stick to Edge despite the constant annoyances Microsoft throws my way. That, and the fact I can still hide most annoying things (like the tools sidebar and bing chat and stuff.
Has has also gotten split screen tabs which is awesome, though I keep forgetting about it and don't use it.
Vertical tabs aren't a good reason to stick with Edge. Vivaldi is better and supports vertical tabs, but is still Chromium. If you want a Firefox based browser with vertical tabs there is Floorp.
I tried to switch to switch to Floorp and while it is pretty good, there are things like tab pinning and tiling that work so much better in Vivaldi (compared to every other browser I've tried) that keeps me there.
