I just installed a really useful FireFox addon: Tree Style Tab. It allows you to place your tabs on the top (default), left sidebar, right sidebar, or bottom. For me, it's the option to put the tabs on either sidebar that's most useful. My screen resolution is 1440. Since most websites have a max resolution of 1024, there's still a lot of space left for either sidebar. Having the tabs on there not only allows me to have more viewable tabs (longer vertical space), but also allows me to see more of the titles on those tabs (wider horizontal space). This is very convenient when I'm choosing stories to feature on Wopular. Another nice feature is that new links open as a child of the originating page so it's easy to keep track of. My prefer position is the right sidebar; that way, it doesn't conflict with my bookmarks.
I'm surprised that this addon has been around for almost two years. I've been searching for it for almost a year. I finally found it from an article on Mashable. The latest verion works with FireFox 3.0; if you're on 3.5, you're out of luck. Well, if you're on 3.5, you should downgrade anyway because of the freezing issues.