Different people respond better to different ways of working. Frankly, looking something up and then closing it drivers me utterly crazy - since I'm the kind of person that forgets about something once they can't see it. Doorway amnesia, out of sight, out of mind and all that. Please don't assume that because you find the "having lots of tabs" approach not your cup of tea that everyone is like that.
I suspect that much like the GP I've got a highly spatial memory, so I'll know pretty instinctively that the web GUI for the SAN was opened about 15 tabs to the left of where I am now. I'll know that cluster of about ten tabs over yonder is where I'm keeping some pages open for the IRPStackSize issue I'm looking at - stuff I might have had a fix applied but will want to keep my reference docs on hand after the users get back to me with testing reports in 48hrs time - because not all problems are things where I can go "there, I've fixed it, don't need to think about it again now". Going to the lengths of categorising it as a bookmark for something that you might only need once is a lot of overhead, and relying on page content search in the address bar doesn't give me context of whether it was a page I had open that had useful information on it, or whether it was useless fluff that happened to have a particular term in it. So keeping some windows/tabs open for comparatively long periods of time is what works best for me.
I don't like to use tree-style tabs or tab grouping as I find them visually cluttered.
Unlike the GP however, personally I haven't had any significant problems with FF27 and ninety hojillion tabs. I used to be one of those FF users who would continually bitch and moan about resource usage (because my FF would hit the 1.8GB ceiling every 24-48hrs and either slow to a crawl or crash) but since about version 20 or 24 or something, memory utilisation has dropped - both in the amount of memory used for particular dataset and the amount at which the memory bloats/leaks/fragments over time. Commit rarely goes over 1GB now (although when it does it usually means FF will soon need to be restarted). my biggest problems with FF now are its inherently single-threaded nature; load a set of tabs for certain websites and you'll often see a core pegged at 100% for 30s or more. Annoying.
All the above is YMMV, my 2 pence, etc.