Lifehacker blog has published a good tip on duplicating current tab page and its history in Firefox 3. To duplicate the current tab page, hold the control key while you drag and drop the current tab on the free area next to tabs.
Ctrl+Drag a Tab to Copy It and Its History [Lifehacker]
2 thoughts on “How To Duplicate Current Tab Page and Its History In Firefox 3”
Edit: Need to add, it work if you only have 1 tab. Else it will open the last tab in a new tab.
Ctrl+Shift+T will open current page in a new tab.