Weird stuff happens on the YouTube webpage. My mom called me for help the other day because she couldn't connect to YouTube. She said the YouTube screen partial

Weird stuff happens on the YouTube webpage. My mom called me for help the other day because she couldn't connect to YouTube. She said the YouTube screen partially loaded, but it said she was offline. What? That doesn't make sense. How does a website load and tell you you're offline; if I was offline how are you telling me that I'm offline? But sure enough, the YouTube app (a single-page application or whatever it is) was loading partially and showing an error telling the user that they were offline. This was with Firefox.