Yes the "+" key open another tab but let's imagine that I have 10 tabs and I would like to duplicate my second or third tab. Without moving them to the far right, close to the "+".
To get something like this (in Firefox).

For example, in Firefox there is an entry in the context menu:

> Also, when I middle-click on a folder (already open in Explorer) to open it again, it doesn't open a new tab with that folder, but instead forces me back to the tab where the folder is already open. Do you see the point? ^^