I think many of us are also aware that saving a bookmark, whether in the browser or to something like pinboard.in, is an invitation to lose it in a back hole. Whereas if it's at least theoretically in "working memory" we want to keep it as a tab. But AFAIK there isn't a really good tool--and certainly not native to a browser as far as I can tell--that lets me quickly and easily rationalize all my tabs into coherent working sets. e.g. Project X, Project Y, email/calendar/etc., to read, and so forth.
TreeStyleTabs in Firefox (which is a great tool regardless of bookmarking), keeps track of parent/child relationships, you can drag & drop into subsets to create the relationship you're talking about, and has a "Bookmark this tree" feature, which would create a folder with subfolders with the top level named as you choose.
(I use the heck out of this, both for the extra vertical space that comes from hiding the top tab bar, and for the conceptual organization that it provides).
