Fan of vertical tabs here, it’s a major boon for how I browse, which tends to involve a number of long-running tasks. Tabs work better than this than bookmarks, because cleaning out bookmarks sucks with how undeveloped all browser bookmark managers somehow still are in 2024.

I’m not too partial to nested tabs, but I think “panes” (Firefox extension Sidebery nomenclature) or “spaces” (what Arc calls them) where you can swap what group of tabs (including pinned tabs) is represented by the tab sidebar with a click is powerful, particularly combined with association of a pane/space with a browser profile.

So for example, a single browser window can switch between being dedicated to general browsing, shopping, online university courses, or software development, and if I want to split a pane/space into a new window temporarily, this is possible too.