One of the features that I loved about the Opera browser was the Duplicate Tab feature which came pre-installed with Opera. Looking up ways on how to implement this in Firefox, I discovered two options:

1. Go to the address bar of the tab you want to duplicate and press Altl+Enter, and voila, you have a duplicate tab. (This process also works for Internet Explorer.)
2. Or you can download the Duplicate Add-on for Firefox. This has the added advantage of adding on your right-click menu -- similar to Opera -- a Duplicate to New Tab or Window, and an extra option of merging all your open Firefox windows. (With merge, just be careful you're not encoding on the rich-text editor of your browser or you'll lose your data, just as I did.)