For example, if I run the following from my browser console on musicbrainz.org:

$.getJSON("https://critiquebrainz.org/ws/1/review/?release_group=7e9abe51-9808-4f18-b88a-f40e9b31f303", function(data)

{ console.log("done") }

).fail(function()

{ console.log("failed")}

);

I get:

XMLHttpRequest cannot load https://critiquebrainz.org/ws/1/review/?release_group=7e9abe51-9808-4f18-b88a-f40e9b31f303. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://musicbrainz.org' is therefore not allowed access.