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EDIT: Solved by Ben

Getting this error. Don't know why. I am trying to have a dropdown, I had it working in the past. 

How it should look: 
http://prntscr.com/eewe7u

Right now I just click on it and nothing happens:
http://prntscr.com/eewefg


Uncaught ReferenceError: Class is not defined
    at popup_menu.js:1


tabcontent.js:14 
Uncaught TypeError: Cannot read property 'getElementsByTagName' of null
    at ddtabcontent (tabcontent.js:14)
    at index.php:888

try adding this <script src="https://ajax.googleapis.com/ajax/libs/prototype/1.7.2.0/prototype.js"></script>