--- a/dom/u2f/U2F.cpp
+++ b/dom/u2f/U2F.cpp
@@ -301,34 +301,16 @@ U2F::ValidAppID(/* in/out */ nsString& a
     return false;
   }
 
   // If the facetId and the appId auths match, accept
   if (facetAuth == appIdAuth) {
     return true;
   }
 
-  nsAutoCString appIdTld;
-  nsAutoCString facetTld;
-
-  rv = tldService->GetBaseDomainFromHost(appIdAuth, 0, appIdTld);
-  if (NS_WARN_IF(NS_FAILED(rv))) {
-    return false;
-  }
-  rv = tldService->GetBaseDomainFromHost(facetAuth, 0, facetTld);
-  if (NS_WARN_IF(NS_FAILED(rv))) {
-    return false;
-  }
-
-  // If this AppID's registered domain matches the Facet's, accept
-  if (!facetTld.IsEmpty() && !appIdTld.IsEmpty() &&
-      (facetTld == appIdTld)) {
-    return true;
-  }
-
   // TODO(Bug 1244959) Implement the remaining algorithm.
   return false;
 }
 
 template <class CB, class Rsp>
 void
 SendError(CB& aCallback, ErrorCode aErrorCode)
 {

--- a/dom/u2f/tests/test_frame_appid_facet.html
+++ b/dom/u2f/tests/test_frame_appid_facet.html
@@ -46,21 +46,13 @@ u2f.register("https://example.com/appId"
 // Test: Dynamic origin
 u2f.register(window.location.origin + "/otherAppId", [{
   version: version,
   challenge: bytesToBase64UrlSafe(challenge),
 }], [], function(res){
   local_is(res.errorCode, 0, "Direct window origin should work");
 });
 
-// eTLD+1 check
-u2f.register("https://test1.example.com/appId", [{
-  version: version,
-  challenge: bytesToBase64UrlSafe(challenge),
-}], [], function(res){
-  local_is(res.errorCode, 0, "Subdomain AppID should work");
-});
-
 local_finished();
 
 </script>
 </body>
 </html>

--- a/dom/u2f/tests/test_frame_appid_facet_subdomain.html
+++ b/dom/u2f/tests/test_frame_appid_facet_subdomain.html
@@ -8,28 +8,53 @@
 <script class="testbody" type="text/javascript">
 "use strict";
 
 var version = "U2F_V2";
 var challenge = new Uint8Array(16);
 
 local_is(window.location.origin, "https://test1.example.com", "Is loaded correctly");
 
-// eTLD+1 check
-u2f.register("https://example.com/appId", [{
+// same domain check
+u2f.register("https://test1.example.com/appId", [{
   version: version,
   challenge: bytesToBase64UrlSafe(challenge),
 }], [], function(res){
-  local_is(res.errorCode, 0, "AppID should work from a subdomain");
+  local_is(res.errorCode, 0, "AppID should work from a subfolder of this domain");
+  step2();
 });
 
-u2f.register("https://example.net/appId", [{
-  version: version,
-  challenge: bytesToBase64UrlSafe(challenge),
-}], [], function(res){
-  local_isnot(res.errorCode, 0, "AppID should not work from other domains");
-});
+function step2() {
+  // same domain check, but wrong scheme
+  u2f.register("http://test1.example.com/appId", [{
+    version: version,
+    challenge: bytesToBase64UrlSafe(challenge),
+  }], [], function(res){
+    local_isnot(res.errorCode, 0, "AppID should work from a subfolder of this domain");
+    step3();
+  });
+}
 
-local_finished();
+function step3() {
+  // eTLD+1 subdomain check
+  u2f.register("https://example.com/appId", [{
+    version: version,
+    challenge: bytesToBase64UrlSafe(challenge),
+  }], [], function(res){
+    local_isnot(res.errorCode, 0, "AppID should not work from another subdomain in this registered domain");
+    step4();
+  });
+}
+
+function step4() {
+  // other domain check
+  u2f.register("https://mochi.test:8888/appId", [{
+    version: version,
+    challenge: bytesToBase64UrlSafe(challenge),
+  }], [], function(res){
+    local_isnot(res.errorCode, 0, "AppID should not work from other domains");
+    local_finished();
+  });
+}
 
 </script>
 </body>
 </html>