I do not know Vivaldi, but I live and die by Tree-Style Tabs. It puts the tabs on the side and arranged them in trees that can be managed as groups. It's the add-on that has kept me on Firefox.
I'm not sure if the entire functionality can really be replicated, but Firefox does have a pretty good add-on selection, maybe you can find one that suits your needs.
Because this is not the first time I've heard about Vivaldi tab management, I looked over a couple videos and it really seems impressive, props to them for doing something really cool in this department. However I know myself, and I'd use maybe half the features that are present, most likely even less. If this is also true for you, I'm almost sure a Firefox add-on could be a suitable replacement:
At the end of the day you obviously don't need to switch if you don't want to, I would just be really amazed if it turned out the main tab mgmt features from Vivaldi were never added to an add-on.
You can just pry Vivaldi out of my cold, dead hands. No other browser comes close to its customisability. As long as it runs adblockers and sponsor block, I'm using it.