XML Parsing Error: no root element found

[henrythe9]

XML Parsing Error: no root element found
Location: https://runkit.com/api/embed/wgdx61057szl?access-key=14b3f00e-af69-4fca-b6be-a695ed628124
Line Number 1, Column 1:

Testing rtc-quickconnect with Runkit on Firefox causes above error in console window (Windows 2007 OS)
Possible suggestions for this error can be found here:
https://forums.asp.net/t/1004395.aspx?What+causes+this+XML+Parsing+Error+no+element+found
https://stackoverflow.com/questions/46487220/xml-parsing-error-no-root-element-found-location-in-console-ff

Not sure if this is an rtc-quickconnect or Firefox issue? Any ideas appreciated?