Quite a few ways are there for duplicating an existing tab in Firefox. Two procedures are pointed out here for your ease:
- Press the reload button (beside the address bar) while holding down the Ctrl key. Or, simply middle-click the mouse. That’d open the current tab in a new tab.
- Another procedure is to press Alt+D, this would set focus in the address bar. Then press Alt+Enter to open the existing/current tab in a new one.