This is very weird and I cannot reproduce it in any way. Can you update to the latest Firefox (75)?
If the problem persists, can you run the following line in the console at the bottom of the Bela IDE:
sed -i 's:// \(printf("connection\):\1SCOPE:' libraries/Scope/Scope.cpp
Then go to your Project Explorer and press the Clean project icon and restart the program. At that point, check that you get a line that says "connectionSCOPE" in your console after the program starts and you refresh the Scope page (this would denote that the Scope websocket has established a connection between the browser and the backend).
Also, can you take another screenshot of the Firefox console after ticking the "XHR" and "Requests" boxes on the top right?