--- a/dom/media/webvtt/vtt.jsm
+++ b/dom/media/webvtt/vtt.jsm
@@ -312,16 +312,20 @@ Cu.import('resource://gre/modules/Servic
 
       // Consume 'n' characters from the input.
       function consume(result) {
         input = input.substr(result.length);
         return result;
       }
 
       var m = input.match(/^([^<]*)(<[^>]+>?)?/);
+      // The input doesn't contain a complete tag.
+      if (!m[0]) {
+        return null;
+      }
       // If there is some text before the next tag, return it, otherwise return
       // the tag.
       return consume(m[1] ? m[1] : m[2]);
     }
 
     // Unescape a string 's'.
     function unescape1(e) {
       return ESCAPE[e];

deleted file mode 100644
--- a/testing/web-platform/meta/webvtt/webvtt-file-format-parsing/webvtt-cue-text-parsing-rules/tests/entities.html.ini
+++ /dev/null
@@ -1,60 +0,0 @@
-[entities.html]
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1307710
-  type: testharness
-  [WebVTT cue data parser test entities - 3686fc0cdc60dc536e75df054b0bd372273db2cc]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - f1869f6e2853635eec81cc3afa3e2b8148ccbdc0]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 92d76530d723b6b4e4ef8280c01cf1c80f9bebdb]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 261cd4e9df4a12535b66a0c39e9635aab2bb19aa]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 1a2269cdb73bf97ec6a99b0edabfe646c471b67e]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 44ceb90884cceeeccb4f7024e3598f7dc5ceebfa]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 05def72af03fc2b1617da950d871b9fd0ba20e5a]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - da999a55445eca43aa41e039ec439c1a812db297]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 0fd9e3823b62c028c1d50e35b1f3ee3df02a62eb]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - e7387003fbacb22b706796c98b781eb4ebf5ff85]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 216cd0e914b9f2ccd04eff6d02a0b1ce24441d95]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 2cdf20980d17a5d077299215e6a7e97f3c6b07e2]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 83f4500c0bd8598480713997a041d8f70fd3f11e]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 2c6b2ba38a08eca45370f28a5b7df2aa463fb3dc]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - f4bb977c0a06851bdd19260c035a766c5c8ea093]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - b1fff1ac42688d16e00f6c758d84e5152e39702d]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - bd68f6beda2c2264e61dff7359c1ad48bc0a9934]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 5b77a0be23453dfe6eea59d43bb0708f89e1df82]
-    expected: FAIL
-
-  [WebVTT cue data parser test entities - 87986551b0e6180cb279f2aa4cdddf77daa90c11]
-    expected: FAIL
-

deleted file mode 100644
--- a/testing/web-platform/meta/webvtt/webvtt-file-format-parsing/webvtt-cue-text-parsing-rules/tests/tags.html.ini
+++ /dev/null
@@ -1,27 +0,0 @@
-[tags.html]
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1307710
-  type: testharness
-  [WebVTT cue data parser test tags - 9dd187edd10c907e6b92148fd82940e401dbe79f]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - 2d2c4333983e23a4962083e8120e5d42c839f77b]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - 2fdc1b84ba41ec98833851e80781df1fbe72182f]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - 487690a6f5da4666f9caaf3a3ecc10992aca1414]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - 0d7df935b172f2a1b357b94596d68f2443f30f8b]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - cd1d6dd274e03ae8fc56bc4ef163998d9ff24496]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - fca1a11d42b735453117f42456360e88082a3fd7]
-    expected: FAIL
-
-  [WebVTT cue data parser test tags - fe3b6277edf5c2f84e7a6779eddd0cac30552bca]
-    expected: FAIL
-