--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -391,17 +391,17 @@ TrackBuffersManager::DoEvictData(const T
       }
       partialEvict = 0;
     }
     if (frame->mTime <= upperLimit.ToMicroseconds()) {
       break;
     }
     partialEvict += sizeof(*frame) + frame->mSize;
   }
-  if (lastKeyFrameIndex < buffer.Length()) {
+  if (lastKeyFrameIndex + 1 < buffer.Length()) {
     CodedFrameRemoval(
       TimeInterval(TimeUnit::FromMicroseconds(buffer[lastKeyFrameIndex+1]->mTime),
                    TimeUnit::FromInfinity()));
   }
 }
 
 nsRefPtr<TrackBuffersManager::RangeRemovalPromise>
 TrackBuffersManager::CodedFrameRemovalWithPromise(TimeInterval aInterval)
@@ -1445,31 +1445,34 @@ TrackBuffersManager::ProcessFrame(MediaR
     MOZ_ASSERT(trackBuffer.mNextInsertionIndex.ref() == 0 ||
                data[trackBuffer.mNextInsertionIndex.ref()]->mTrackInfo->GetID() == data[trackBuffer.mNextInsertionIndex.ref()-1]->mTrackInfo->GetID() ||
                data[trackBuffer.mNextInsertionIndex.ref()]->mKeyframe);
     trackBuffer.mNextInsertionIndex.ref()++;
   } else if (presentationTimestamp < trackBuffer.mBufferedRanges.GetStart()) {
     data.InsertElementAt(0, aSample);
     MOZ_ASSERT(aSample->mKeyframe);
     trackBuffer.mNextInsertionIndex = Some(size_t(1));
-  } else if (presentationTimestamp >= trackBuffer.mBufferedRanges.GetEnd()) {
-    data.AppendElement(aSample);
-    MOZ_ASSERT(data.Length() <= 2 ||
-               data[data.Length()-1]->mTrackInfo->GetID() == data[data.Length()-2]->mTrackInfo->GetID() ||
-               data[data.Length()-1]->mKeyframe);
-    trackBuffer.mNextInsertionIndex = Some(data.Length());
   } else {
     // Find which discontinuity we should insert the frame before.
     TimeInterval target;
     for (const auto& interval : trackBuffer.mBufferedRanges) {
       if (presentationTimestamp < interval.mStart) {
         target = interval;
         break;
       }
     }
+    if (target.IsEmpty()) {
+      // No existing ranges found after our frame presentation time.
+      // Insert frame at the end of array.
+      data.AppendElement(aSample);
+      MOZ_ASSERT(data.Length() <= 2 ||
+                 data[data.Length()-1]->mTrackInfo->GetID() == data[data.Length()-2]->mTrackInfo->GetID() ||
+                 data[data.Length()-1]->mKeyframe);
+      trackBuffer.mNextInsertionIndex = Some(data.Length());
+    }
     for (uint32_t i = 0; i < data.Length(); i++) {
       const nsRefPtr<MediaRawData>& sample = data[i];
       TimeInterval sampleInterval{
         TimeUnit::FromMicroseconds(sample->mTime),
         TimeUnit::FromMicroseconds(sample->GetEndTime())};
       if (target.Intersects(sampleInterval)) {
         data.InsertElementAt(i, aSample);
         MOZ_ASSERT(i != 0 &&