1. Load data:application/json,[{"actor":true,"preview":{"nodeType":8}}] 2. Click the 0 property 3. The subtree collapses and shows "<!-- undefined -->" instead of "Object". This is because Reps accesses the object. Either Reps should not be touching the object at all, or JSON Viewer should not give the object to Reps this way. https://dxr.mozilla.org/mozilla-central/rev/45fde181a497a187d01d5412f5b72897c7520517/devtools/client/shared/components/reps/reps.js#2266 function supportsObject(object, type) { if (!isGrip(object)) { return false; } return object.preview && object.preview.nodeType === nodeConstants.COMMENT_NODE; }

Thanks for the report! This will be fixed with bug 1377668 Honza