Bug 1450565 use GET for initial authorization request, r=mossop

MozReview-Commit-ID: 70PQSeoxvOF

--HG--
extra : rebase_source : e35e5f5d9e3cea22776078ffdb3085ffe61ba99e

toolkit/components/extensions/parent/ext-identity.js

@@ -14,7 +14,7 @@ var {
 const checkRedirected = (url, redirectURI) => {
   return new Promise((resolve, reject) => {
     let xhr = new XMLHttpRequest();
-    xhr.open("HEAD", url);
+    xhr.open("GET", url);
     // We expect this if the user has not authenticated.
     xhr.onload = () => {
       reject(0);