diff --git a/dom/canvas/ImageBitmap.cpp b/dom/canvas/ImageBitmap.cpp
index d7df938aaa..2db97dd6b2 100644
--- a/dom/canvas/ImageBitmap.cpp
+++ b/dom/canvas/ImageBitmap.cpp
@@ -1561,43 +1561,5 @@ ImageBitmap::ExtensionsEnabled(JSContext* aCx, JSObject*)
   }
 }
 
-// ImageBitmap extensions.
-ImageBitmapFormat
-ImageBitmap::FindOptimalFormat(const Optional<Sequence<ImageBitmapFormat>>& aPossibleFormats,
-                               ErrorResult& aRv)
-{
-  MOZ_ASSERT(mDataWrapper, "No ImageBitmapFormatUtils functionalities.");
-
-  ImageBitmapFormat platformFormat = mDataWrapper->GetFormat();
-
-  if (!aPossibleFormats.WasPassed() ||
-      aPossibleFormats.Value().Contains(platformFormat)) {
-    return platformFormat;
-  } else {
-    // If no matching is found, FindBestMatchingFromat() returns
-    // ImageBitmapFormat::EndGuard_ and we throw an exception.
-    ImageBitmapFormat optimalFormat =
-      FindBestMatchingFromat(platformFormat, aPossibleFormats.Value());
-
-    if (optimalFormat == ImageBitmapFormat::EndGuard_) {
-      aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
-    }
-
-    return optimalFormat;
-  }
-}
-
-int32_t
-ImageBitmap::MappedDataLength(ImageBitmapFormat aFormat, ErrorResult& aRv)
-{
-  MOZ_ASSERT(mDataWrapper, "No ImageBitmapFormatUtils functionalities.");
-
-  if (aFormat == mDataWrapper->GetFormat()) {
-    return mDataWrapper->GetBufferLength();
-  } else {
-    return CalculateImageBufferSize(aFormat, Width(), Height());
-  }
-}
-
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/canvas/ImageBitmap.h b/dom/canvas/ImageBitmap.h
index efd339f112..77fc9e1aa8 100644
--- a/dom/canvas/ImageBitmap.h
+++ b/dom/canvas/ImageBitmap.h
@@ -153,14 +153,6 @@ public:
     return mWriteOnly;
   }
 
-  // Mozilla Extensions
-  ImageBitmapFormat
-  FindOptimalFormat(const Optional<Sequence<ImageBitmapFormat>>& aPossibleFormats,
-                    ErrorResult& aRv);
-
-  int32_t
-  MappedDataLength(ImageBitmapFormat aFormat, ErrorResult& aRv);
-
 protected:
 
   /*
diff --git a/dom/canvas/ImageBitmapUtils.cpp b/dom/canvas/ImageBitmapUtils.cpp
index d6f249468f..72b73729cd 100644
--- a/dom/canvas/ImageBitmapUtils.cpp
+++ b/dom/canvas/ImageBitmapUtils.cpp
@@ -2728,16 +2728,6 @@ GetChannelCountOfImageFormat(ImageBitmapFormat aFormat)
   return format->GetChannelCount();
 }
 
-uint32_t
-CalculateImageBufferSize(ImageBitmapFormat aFormat,
-                         uint32_t aWidth, uint32_t aHeight)
-{
-  UtilsUniquePtr format = Utils::GetUtils(aFormat);
-  MOZ_ASSERT(format, "Cannot get a valid ImageBitmapFormatUtils instance.");
-
-  return format->NeededBufferSize(aWidth, aHeight);
-}
-
 UniquePtr<ImagePixelLayout>
 CopyAndConvertImageData(ImageBitmapFormat aSrcFormat,
                         const uint8_t* aSrcBuffer,
diff --git a/dom/canvas/ImageBitmapUtils.h b/dom/canvas/ImageBitmapUtils.h
index dfde52e07b..24fb201804 100644
--- a/dom/canvas/ImageBitmapUtils.h
+++ b/dom/canvas/ImageBitmapUtils.h
@@ -48,14 +48,6 @@ CreatePixelLayoutFromPlanarYCbCrData(const layers::PlanarYCbCrData* aData);
 uint8_t
 GetChannelCountOfImageFormat(ImageBitmapFormat aFormat);
 
-/*
- * Get the needed buffer size to store the image data in the given
- * ImageBitmapFormat with the given width and height.
- */
-uint32_t
-CalculateImageBufferSize(ImageBitmapFormat aFormat,
-                         uint32_t aWidth, uint32_t aHeight);
-
 /*
  * This function always copies the image data in _aSrcBuffer_ into _aDstBuffer_
  * and it also performs color conversion if the _aSrcFormat_ and the
diff --git a/dom/webidl/ImageBitmap.webidl b/dom/webidl/ImageBitmap.webidl
index 14e0c1165b..73f61f59ed 100644
--- a/dom/webidl/ImageBitmap.webidl
+++ b/dom/webidl/ImageBitmap.webidl
@@ -394,9 +394,3 @@ dictionary ChannelPixelLayout {
 
 typedef sequence<ChannelPixelLayout> ImagePixelLayout;
 
-partial interface ImageBitmap {
-    [Throws, Func="mozilla::dom::ImageBitmap::ExtensionsEnabled"]
-    ImageBitmapFormat               findOptimalFormat (optional sequence<ImageBitmapFormat> aPossibleFormats);
-    [Throws, Func="mozilla::dom::ImageBitmap::ExtensionsEnabled"]
-    long                            mappedDataLength (ImageBitmapFormat aFormat);
-};