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Vivaldi's tab tilling add-on in Firefox
(lemmy.dbzer0.com)
A place to discuss the news and latest developments on the open-source browser Firefox
Not exactly what you are looking for but Sidebery has a feature called Snapshots that allow you to save a group of tabs in their current state to open them later.
That's more of an alternative to vivaldi sessions, not workspaces
Interesting. I'll need to test it to see how it exactly behaves.