Youtube video download video quality

I am using a new program called Xtreme Download Manager to schedule Youtube video downloads at a later time. When I open the video that I want to download the Xtreme Download Manager popup box displays with the video quality formats that I can choose from to download it in. The problem is that the video formats are not what I want such as the highest it will display is MP4 in 480p. I want to download it in 1080p. At the bottom of the display box there is a button called More Formats. When I click on it it displays another box that says, " Please select the desired format in your browser's video player." Where do I go in Firefox to able to tell it which formats to allow it to display? Please help me.