Here's a hint: there's no difference between bookmarks, open tabs (read or unread), and page history.
There is a very big difference to those of us who don't have persistent Internet connections. Because of a rather unique social situation, I spend a lot of my time house-sitting at the home of a family member who died recently. I have DSL at my own home, but that place has nothing except electricity, water, and gas.
The result is that I tend to grab a large number of pages from my home connection on my laptop, keep them as open tabs, and read through them when I am away from home. An RSS reader like Brief (a Firefox extension) is also useful for this method of short-term information storage.
My conclusion: an open tab (or a page successfully saved to disk) is something you can use whenever you want, but a bookmark is something you can only reach when you are connected to the Internet.
The problem I see with this is performance. Currently, Firefox tends to get really slow on Linux with multiple tabs open.