Until I saw this post , I was sorely missing the duplicate tab for firefox. It was near the top of my most loved firefox extensions till firefox 2.x. The addons page for this extension said it does not support 3.5. Well, and then I learnt 3.5 has a built in duplicate tab feature.
Just press the ctrl key and hold the tab you want to duplicate, drag and drop it to the place/area you want the new duplicate tab to appear. And thats it!!..
Life is simple now 🙂