--- a/content/html/content/src/nsTimeRanges.cpp
+++ b/content/html/content/src/nsTimeRanges.cpp
@@ -70,16 +70,20 @@ nsTimeRanges::Normalize()
   if (mRanges.Length() >= 2) {
     nsAutoTArray<TimeRange,4> normalized;
 
     mRanges.Sort(CompareTimeRanges());
 
     // This merges the intervals.
     TimeRange current(mRanges[0]);
     for (PRUint32 i = 1; i < mRanges.Length(); i++) {
+      if (current.mStart <= mRanges[i].mStart &&
+          current.mEnd >= mRanges[i].mEnd) {
+        continue;
+      }
       if (current.mEnd >= mRanges[i].mStart) {
         current.mEnd = mRanges[i].mEnd;
       } else {
         normalized.AppendElement(current);
         current = mRanges[i];
       }
     }
 

--- a/content/media/test/test_played.html
+++ b/content/media/test/test_played.html
@@ -69,17 +69,22 @@ var tests = [
 
 // Play the first half of the file, seek back, while
 // continuing to play. We shall have only one range.
 {
   setup : function (element) {
     let onTimeUpdate = function() {
       if (element.currentTime > element.duration/2) {
         element.removeEventListener("timeupdate", onTimeUpdate, false);
+        element.pause();
+        var oldEndRange = element.played.end(0);
         element.currentTime = element.duration / 4;
+        is(element.played.end(0), oldEndRange,
+            "When seeking back, |played| should not be changed");
+        element.play();
       }
     }
     element.addEventListener("timeupdate", onTimeUpdate, false);
     check_full_file_played(element);
     element.play();
   }
 },