thank you for the swift reply.
Actually you are right, on the right side (the pdf rendering of the text on the left) the dictionaries work properly.
I was trying to make it work on the left in order to be able to look up words using the comment feature of overleaf, thus looking up words absent from the actual text, but pertaining to the original.
Now I see that even there, right-clicking on a word it does open a Firefox menu, only, the word is not copied there (I do not know if it is meant to be) and searched, the search window is empty.
However, to do so I can go to a tab where I have a dictionary open!
Another very good German dictionary is: https://www.dwds.de
Thank you for the good work,