There’s loads of add-ons that can help you duplicate tabs in Firefox, even copying all of the history to the new tab. What you might not realize, however, is that you can do the same thing without any add-ons.
To duplicate a tab, all you need to do is hold down the Ctrl key while dragging the tab to a new spot on your tab bar–you’ll see the little arrow show up, and you can drop the tab there. Once you’ve done so, you’ll see that the tab has been duplicated, including all of the tab history. Useful! [via Help Desk Geek]