Visiting https://googlewebcomponents.github.io/model-viewer/test/fidelity/results-viewer.html, I see the message Loading... and the console shows a 404 for config.json.
Looks like we accidentally stopped publishing them to gh-pages at some point...
Appears to be broken again. 馃檭
Yah, looks like our CI is having a day. I'm diagnosing the issue now. Thanks for the heads up 馃憤
This is fixed again as of https://github.com/GoogleWebComponents/model-viewer/commit/42ae83213eceb70185390b0c1c866ff9b318ec68