No prob! I did use Tree Style Tabs and that helped a bit but Vivaldi’s extra features and how streamlined it is just edge it out as better than Firefox + addons for me. There’s also tab workspaces for grouping tabs into screens, typically on what type of browsing you’re doing, and tab tiling which Firefox was able to do back in its XUL days but can’t do in Quantum. I think Firefox would be pretty neat with a power-user oriented fork to bring back some missing features.
My only issue with Vivaldi is, if a site is still providing insecure HTTP for whatever reason (7digital for some reason still provides purchase downloads this way) then Vivaldi silently fails. Firefox clearly warns the user, so that’s my reason for having Firefox on hand - for those stragglers.