I thought tab candy for FF was very useful.
I am trying to get used to using Opera's Tab Stcking to arrange pages from a site.
For instance, using WebmasterWorld as one tab, Bing as another, PubCon, and Twitter as another. It seems like this should work 'in theory', but I have yet to get a grasp on the usability here. I am always trying to 'find that page'.