Posting a message to EventHubs from JavaScript in Firefox results in an "element not found" error.
The reason for this looks to be a bug in Firefox as described here: https://bugzilla.mozilla.org/show_bug.cgi?id=884693
It seems that Firefox is not able to handle an empty response which has a Content-Type header that contains "application/xml; charset=utf-8". Firefox tries to parse parse the empty response as an XML document but cannot find the root element (hence the element not found error).
I know this is a bug in Firefox as other browsers handle this case correctly, but should the response type really be "application/xml". If the response is empty wouldn't it make more sense to set the Content-Type to "text/plain" instead?