--- a/dom/media/webvtt/WebVTTParserWrapper.js
+++ b/dom/media/webvtt/WebVTTParserWrapper.js
@@ -46,17 +46,17 @@ WebVTTParserWrapper.prototype =
     this.parser.onparsingerror = function(e) {
       // Passing the just the error code back is enough for our needs.
       callback.onParsingError(("code" in e) ? e.code : -1);
     };
   },
 
   convertCueToDOMTree: function(window, cue)
   {
-    return WebVTT.convertCueToDOMTree(window, cue.text);
+    return WebVTT.convertCueToDOMTree(window, cue);
   },
 
   processCues: function(window, cues, overlay, controls)
   {
     WebVTT.processCues(window, cues, overlay, controls);
   },
 
   classDescription: "Wrapper for the JS WebVTT implementation (vtt.js)",

--- a/dom/media/webvtt/vtt.jsm
+++ b/dom/media/webvtt/vtt.jsm
@@ -298,17 +298,19 @@ Cu.import('resource://gre/modules/Servic
     lang: "lang"
   };
 
   var NEEDS_PARENT = {
     rt: "ruby"
   };
 
   // Parse content into a document fragment.
-  function parseContent(window, input, bReturnFrag) {
+  function parseContent(window, cue, bReturnFrag) {
+    var input = cue.text;
+    var validTimeRange = {start: cue.startTime, end: cue.endTime};
     function nextToken() {
       // Check for end-of-string.
       if (!input) {
         return null;
       }
 
       // Consume 'n' characters from the input.
       function consume(result) {
@@ -377,16 +379,27 @@ Cu.import('resource://gre/modules/Servic
       if (f[1]) {
         f = f[1].slice(0, 3).padEnd(3, "0");
       } else {
         f = "000";
       }
       return hours + ':' + minutes + ':' + seconds + '.' + f;
     }
 
+    // Check the input ts against to validTimeRange[] and also update
+    // validTimeRange.
+    function isValidTimestamp(ts) {
+    dump(validTimeRange["start"]  +" " +ts+ " "+validTimeRange["end"] +"\n");
+      if (validTimeRange["start"] <= ts && ts <= validTimeRange["end"]) {
+        validTimeRange["start"] = ts;
+        return true;
+      }
+      return false;
+    }
+
     var root;
     if (bReturnFrag) {
       root = window.document.createDocumentFragment();
     } else {
       root = window.document.createElement("div");
     }
     var current = root,
         t,
@@ -401,18 +414,22 @@ Cu.import('resource://gre/modules/Servic
             tagStack.pop();
             current = current.parentNode;
           }
           // Otherwise just ignore the end tag.
           continue;
         }
         var ts = collectTimeStamp(t.substr(1, t.length - 1));
         var node;
+        // Timestamps are lead nodes as well.
         if (ts) {
-          // Timestamps are lead nodes as well.
+          if (!bReturnFrag && !isValidTimestamp(ts)) {
+            // rendering and the ts is invalid
+            continue;
+          }
           node = window.document.createProcessingInstruction("timestamp", normalizedTimeStamp(ts));
           current.appendChild(node);
           continue;
         }
         var m = t.match(/^<([^.\s/0-9>]+)(\.[^\s\\>]+)?([^>\\]+)?(\\?)>?$/);
         // If we can't parse the tag, skip to the next tag.
         if (!m) {
           continue;
@@ -477,17 +494,17 @@ Cu.import('resource://gre/modules/Servic
       backgroundColor = "rgb(0, 0, 0)";
     }
 
     StyleBox.call(this);
     this.cue = cue;
 
     // Parse our cue's text into a DOM tree rooted at 'cueDiv'. This div will
     // have inline positioning and will function as the cue background box.
-    this.cueDiv = parseContent(window, cue.text, false);
+    this.cueDiv = parseContent(window, cue, false);
     var styles = {
       color: color,
       backgroundColor: backgroundColor,
       position: "relative",
       left: 0,
       right: 0,
       top: 0,
       bottom: 0,
@@ -865,21 +882,21 @@ Cu.import('resource://gre/modules/Servic
         if (typeof data !== "string") {
           throw new Error("Error - expected string data.");
         }
         return decodeURIComponent(encodeURIComponent(data));
       }
     };
   };
 
-  WebVTT.convertCueToDOMTree = function(window, cuetext) {
+  WebVTT.convertCueToDOMTree = function(window, cue) {
     if (!window) {
       return null;
     }
-    return parseContent(window, cuetext, true);
+    return parseContent(window, cue, true);
   };
 
   var FONT_SIZE_PERCENT = 0.05;
   var FONT_STYLE = "sans-serif";
   var CUE_BACKGROUND_PADDING = "1.5%";
 
   // Runs the processing model over the cues and regions passed to it.
   // @param overlay A block level element (usually a div) that the computed cues