I've been using Tree Style Tabs[0] with Firefox for a long time. Being able to nest tabs and then collapse them is awesome. It is hard to live without it when using Chrome (I know there is a similar addon for Chrome[1], but it doesn't have the same feel since it just adds a new window off to the side and still has the tabs across the top).
While I love Tree Style Tab, I think separate windows for separate topics is more useful than trees, and I think saving windows/topics as sessions using the Session Manager extension is more useful than bookmarking, especially seeing as how Session Manager supports appending windows to previously saved sessions.
You can flexibly add text to the title bar of each window to name the window as you choose. These names show up in Aero Peek etc. to make switching between windows effortless.
TreeStyleTabs, FireTitle, and a few other FF extensions are what keep me firmly in the FF camp. Its extensibility is the best of all the browsers IMHO.
Sometimes what I think will be a quick search turns into multiple tabs so its really easy to pull a tree into a new window and then save it using Session manager.
Wow, apparently this has been a thing since Firefox 20. This is absolutely wonderful. You can also add the Tab Groups button anywhere from the customize menu.
In addition to that, Firefox handles many tabs very well because it is a single process application and does not use as many resources as Chrome does. Tree Style Tab is the best when you are researching something and you basically keep all open tabs under a single branch. When you are done, you just close all branch.
At this point I'm legitimately unsure how people do web research/search without TST. I know at some point in the far past I did it myself...but I'm not sure how.
+1 for Tree Style Tabs. This seems in the right direction, but it's not nearly as feature packed as TST. One thing with TST though, pinned tabs is broken :(
I love TST, but I find that on my current screen it takes too much space to be actually usable. I suppose it is great for people with relatively small screens where you have browser maximized practically always, and on very large screens where you can still comfortably fit two windows side-by-side even with TST. But I'm stuck firmly in the middle, where maximized browser seems waste, but I can't really fit anything useful on the side if I'm using TST.
The only thing that annoys me about TST is that the various built-in themes really only look good on OS X, because they're typically hard-coded to use colours from the standard OS X theme. If you're using a markedly different theme on another OS, TST varies between weird and unreadable.
Of course, I still use it. Better weird-looking tabs than non-vertical, non-nested tabs at all.
[0] https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta... [1] https://chrome.google.com/webstore/detail/sidewise-tree-styl...