[naiveter]

I'm not a Vivaldi user, but just based off their feature page, you might be interested to check out some of the features/extensions:

1. Firefox's native tab groups [^1]

2. Sidebery's panels (if you don't mind vertical tabs) [^2]

3. Simple Tab Groups [^3]

[1]: https://www.firefox.com/en-US/features/tab-groups/

[2]: https://addons.mozilla.org/en-US/firefox/addon/sidebery/

[3]: https://addons.mozilla.org/en-US/firefox/addon/simple-tab-gr...

[noisy_boy]

I have used tab groups and found then to be basically eating into horizontal tab space, once I created a bunch. Workspaces don't have that problem. I have tried vertical tabs but never felt comfortable with them.