Summary: XMLHttpRequests for web content (and WebExtensions) will now
follow the spec and return a null response/responseXML in the event of
a parsing error, rather than a document with a <parsererror> root. The
web console will also log a more informative error. Non-WebExtension
addons and other chrome code will continue to generate <parsererror>
documents, for backwards compatibility.
Bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=289714
Standard:
https://xhr.spec.whatwg.org/#document-response
Platform coverage: all.
Estimated release: Firefox 50.
Devtools bug: none needed.
Other browsers: Chrome, Safari and Edge already follow the spec behavior.