I personally like tabs a lot, but according to this article many people don't:

Thanks to its extensibility, Firefox quickly became the favorite browser for most power users. But while extensions are a great way to make Firefox more functional, Mozilla's designers are also currently thinking about a complete redesign of the way the browser looks and feels, in order to keep up with changing usage patterns. The most radical proposal we have seen so far would do away with the standard browser tabs, and replace them with an interface that looks more like iTunes