Mozilla the company behind Firefox thinks that the tabbed interface it’s so famous for is reaching the end of it’s lifespan. So they’re launching a design competition to come up with the next big thing in browsers.
Tabs worked well on slow machines on a thin Internet, where ten browser sessions were “many browser sessions”. Today, 20+ parallel sessions are quite common; the browser is more of an operating system than a data display application; we use it to manage the web as a shared hard drive.
— Mozilla Labs
One interesting idea is already floating around from Mozilla Labs, having the tabs on the side instead of the top.