You've got the question wrong. I could say an open tab works like a bookmark without having to organize and delete the bookmarks, but then I have to organize the tabs. Bookmark management is very crude in Firefox without add ons, so I have a tree view in either the tree style tabs or in the bookmark manager, without much of a difference.

But then the pressing question is, why can't most of the tabs not just be closed? Because I haven't read them yet.

So the real question is, why do I open them in the first place and I'm shy of an answer.