On page like https://github.com/rdiez/Tools/blob/master/RDChecksum/rdchecksum.pl you can't Middle-Click on it to scroll up/down but only right/left.
I just opened the page you linked to on a Windows 10 laptop running Firefox, and my middle mouse button scrolls up and down, not right and left.
For me, i can't get it to scroll at all with middle mouse button... I can't get it to bring up the scroll option when I just click it, nor when I push and hold it. I really want to see both of these implemented similarly or exactly as they are in google chrome.