You can middle-click the Reload button on the location bar to open the current page in a new tab.
You can also hold down the Ctrl key and drag the tab to another position on the tab bar.

There are two possible ways to clone a firefox tab in ubuntu:

Using the History:

1) Right clicking on the back/forward buttons of the browser which will open the history of the page. (You can also do the next step directly on the arrows, but if you opened the history you get to choose which page to open from the history, instead of opening directly the previous or next one).

2) Press (and keep pressing) the Ctrl button and click on one of pages in the history. Click on one of the pages with the mouse's middle click button.

3) Now, after doing any of the steps in the second point, it will open a new tab with the same history of the old tab, and the starting page will be the page you've chosen from the history.

Wihout using the History

If you try to drag and drop the tab as if you were re-arranging it, keep holding Ctrl button before releasing the mouse button while dragging the tab. This will do the same as above except that you can get to choose where to clone the tab in the tab-bar, and the starting page of the cloned tab is the same as the original one.

Hope this was helpful. Thank you.

Note that a middle-click on the Reload button and holding down Ctrl and drag a tab will give you a copy of the tab that includes the tab history (Back/Forward).
Holding down the Ctrl key and clicking an entry in the tab history drop-down list will open the highlighted link in a new tab.

Thanks to everyone for your help. Easy enough to do, but difficult to find the "how to."