I don't know why I never vibed with vertical tabs, but I've just never been able to make it work mentally. And I could see a double-edged sword with synced workspaces (I think having a button to click and see open tabs on other devices is a perfect middle ground). Personally, tab groups is the only thing I miss from Chromium. I used the feature for grouping, but also for labeling tabs: "Check back Tuesday," or "Don't forget to follow up," or whatever. If they gave us tab groups and then never updated Firefox again, I think I would be pretty happy.

EDIT: well okay not happy, but I would be satisfied with the browser we ended up with.