You could check out Sidebery (Firefox addon) (A note: I use it with Floorp, a fork of Firefox built around user control. Floorp link)

github

addons.mozilla

Ton of features and very nuanced customization (you can change pretty much all minutia of its UI, which is a huge plus over other stuff I used). Some noteworthy features I like:

• Vertical tab bar with collapsible parent/child tabs

• Tab Grouping, which seems to be functionally the same as workspaces

• Unload or refresh tabs or groups en masse easily

• Customizable new tab buttons. ie: you can have "new tab", "new private (or other container) tab", and "new lemmy.world tab" all at once.

• Customizable movement of tabs to specific Tab Groups based on domain and/or container. ie: I have a "Media" tab group, and I set it up so any domain from youtube.com or dropout.tv automatically get moved from other tab groups over to "Media"

There's more, but those are the points that I find the most useful.