Back out 346bbcaeff38 (bug 1076803) for still failing intermittently.

layout/style/test/test_font_loading_api.html

@@ -307,6 +307,9 @@ function runTest() {
 
   }).then(function() {
 
+    // XXX Disabled this sub-test due to intermittent failures (bug 1076803).
+    return;
+
     // (TEST 18) Test passing valid url() source strings to the FontFace
     // constructor.
     var srcTests = Promise.resolve();