The details are:

Browser: Chrome 47.0.2526 Windows 7

User Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.106 Safari/537.36

Extension: userjs-chrome 5.83.2.

I used to download videos using SaveFrom.net and Tampermonkey extension for chrome. It is disabled almost in every youtube page. The download button is being displayed but when I click on it, I get a "videoplayback.txt" blank file.