Not all pages with .json in the end is really a JSON file. It is especially true for source code viewing. Pages like: https://github.com/w3c/wpt-tools/blob/master/scripts/package.json or https://dxr.mozilla.org/mozilla-central/source/testing/talos/talos.json are perfect html pages, which are treated as JSON and broken on Firefox Developer Edition. This is only reproducible on Firefox Developer Edition, which I guess is because only DE has "devtools.jsonview.enabled" set to true by default. I guess it is a regression from bug 1230544.
2 years ago
Work in progress in bug 1235118. Honza