--- a/dom/base/DOMMatrix.cpp
+++ b/dom/base/DOMMatrix.cpp
@@ -214,17 +214,17 @@ already_AddRefed<DOMMatrixReadOnly> DOMM
       new DOMMatrixReadOnly(aGlobal.GetAsSupports(), is2D);
   SetDataInMatrix(obj, aArray64.Data(), length, aRv);
 
   return obj.forget();
 }
 
 already_AddRefed<DOMMatrixReadOnly> DOMMatrixReadOnly::Constructor(
     const GlobalObject& aGlobal,
-    const Optional<StringOrUnrestrictedDoubleSequence>& aArg,
+    const Optional<StringOrUnrestrictedDoubleSequenceOrDOMMatrixReadOnly>& aArg,
     ErrorResult& aRv) {
   if (!aArg.WasPassed()) {
     RefPtr<DOMMatrixReadOnly> rval =
         new DOMMatrixReadOnly(aGlobal.GetAsSupports());
     return rval.forget();
   }
 
   const auto& arg = aArg.Value();
@@ -235,16 +235,21 @@ already_AddRefed<DOMMatrixReadOnly> DOMM
       aRv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
       return nullptr;
     }
     RefPtr<DOMMatrixReadOnly> rval =
         new DOMMatrixReadOnly(aGlobal.GetAsSupports());
     rval->SetMatrixValue(arg.GetAsString(), aRv);
     return rval.forget();
   }
+  if (arg.IsDOMMatrixReadOnly()) {
+    RefPtr<DOMMatrixReadOnly> obj = new DOMMatrixReadOnly(
+        aGlobal.GetAsSupports(), arg.GetAsDOMMatrixReadOnly());
+    return obj.forget();
+  }
 
   const auto& sequence = arg.GetAsUnrestrictedDoubleSequence();
   const int length = sequence.Length();
   const bool is2D = length == 6;
   RefPtr<DOMMatrixReadOnly> rval =
       new DOMMatrixReadOnly(aGlobal.GetAsSupports(), is2D);
   SetDataInMatrix(rval, sequence.Elements(), length, aRv);
   return rval.forget();
@@ -653,40 +658,49 @@ already_AddRefed<DOMMatrix> DOMMatrix::F
   const int length = aArray64.Length();
   const bool is2D = length == 6;
   RefPtr<DOMMatrix> obj = new DOMMatrix(aGlobal.GetAsSupports(), is2D);
   SetDataInMatrix(obj, aArray64.Data(), length, aRv);
 
   return obj.forget();
 }
 
-already_AddRefed<DOMMatrix> DOMMatrix::Constructor(const GlobalObject& aGlobal,
-                                                   ErrorResult& aRv) {
-  RefPtr<DOMMatrix> obj = new DOMMatrix(aGlobal.GetAsSupports());
-  return obj.forget();
-}
-
 already_AddRefed<DOMMatrix> DOMMatrix::Constructor(
-    const GlobalObject& aGlobal, const nsAString& aTransformList,
+    const GlobalObject& aGlobal,
+    const Optional<StringOrUnrestrictedDoubleSequenceOrDOMMatrixReadOnly>& aArg,
     ErrorResult& aRv) {
-  nsCOMPtr<nsPIDOMWindowInner> win = do_QueryInterface(aGlobal.GetAsSupports());
-  if (!win) {
-    aRv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
-    return nullptr;
+  if (!aArg.WasPassed()) {
+    RefPtr<DOMMatrix> rval = new DOMMatrix(aGlobal.GetAsSupports());
+    return rval.forget();
   }
-  RefPtr<DOMMatrix> obj = new DOMMatrix(aGlobal.GetAsSupports());
-  obj = obj->SetMatrixValue(aTransformList, aRv);
-  return obj.forget();
-}
 
-already_AddRefed<DOMMatrix> DOMMatrix::Constructor(
-    const GlobalObject& aGlobal, const DOMMatrixReadOnly& aOther,
-    ErrorResult& aRv) {
-  RefPtr<DOMMatrix> obj = new DOMMatrix(aGlobal.GetAsSupports(), aOther);
-  return obj.forget();
+  const auto& arg = aArg.Value();
+  if (arg.IsString()) {
+    nsCOMPtr<nsPIDOMWindowInner> win =
+        do_QueryInterface(aGlobal.GetAsSupports());
+    if (!win) {
+      aRv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+      return nullptr;
+    }
+    RefPtr<DOMMatrix> rval = new DOMMatrix(aGlobal.GetAsSupports());
+    rval->SetMatrixValue(arg.GetAsString(), aRv);
+    return rval.forget();
+  }
+  if (arg.IsDOMMatrixReadOnly()) {
+    RefPtr<DOMMatrix> obj =
+        new DOMMatrix(aGlobal.GetAsSupports(), arg.GetAsDOMMatrixReadOnly());
+    return obj.forget();
+  }
+
+  const auto& sequence = arg.GetAsUnrestrictedDoubleSequence();
+  const int length = sequence.Length();
+  const bool is2D = length == 6;
+  RefPtr<DOMMatrix> rval = new DOMMatrix(aGlobal.GetAsSupports(), is2D);
+  SetDataInMatrix(rval, sequence.Elements(), length, aRv);
+  return rval.forget();
 }
 
 template <typename T>
 static void SetDataInMatrix(DOMMatrixReadOnly* aMatrix, const T* aData,
                             int aLength, ErrorResult& aRv) {
   if (aLength == 16) {
     aMatrix->SetM11(aData[0]);
     aMatrix->SetM12(aData[1]);
@@ -713,39 +727,16 @@ static void SetDataInMatrix(DOMMatrixRea
     aMatrix->SetF(aData[5]);
   } else {
     nsAutoString lengthStr;
     lengthStr.AppendInt(aLength);
     aRv.ThrowTypeError<MSG_MATRIX_INIT_LENGTH_WRONG>(lengthStr);
   }
 }
 
-already_AddRefed<DOMMatrix> DOMMatrix::Constructor(const GlobalObject& aGlobal,
-                                                   const Float32Array& aArray32,
-                                                   ErrorResult& aRv) {
-  return FromFloat32Array(aGlobal, aArray32, aRv);
-}
-
-already_AddRefed<DOMMatrix> DOMMatrix::Constructor(const GlobalObject& aGlobal,
-                                                   const Float64Array& aArray64,
-                                                   ErrorResult& aRv) {
-  return FromFloat64Array(aGlobal, aArray64, aRv);
-}
-
-already_AddRefed<DOMMatrix> DOMMatrix::Constructor(
-    const GlobalObject& aGlobal, const Sequence<double>& aNumberSequence,
-    ErrorResult& aRv) {
-  const int length = aNumberSequence.Length();
-  const bool is2D = length == 6;
-  RefPtr<DOMMatrix> obj = new DOMMatrix(aGlobal.GetAsSupports(), is2D);
-  SetDataInMatrix(obj, aNumberSequence.Elements(), length, aRv);
-
-  return obj.forget();
-}
-
 already_AddRefed<DOMMatrix> DOMMatrix::ReadStructuredClone(
     JSContext* aCx, nsIGlobalObject* aGlobal,
     JSStructuredCloneReader* aReader) {
   uint8_t is2D;
 
   if (!JS_ReadBytes(aReader, &is2D, 1)) {
     return nullptr;
   }

--- a/dom/base/DOMMatrix.h
+++ b/dom/base/DOMMatrix.h
@@ -21,17 +21,17 @@
 class nsIGlobalObject;
 
 namespace mozilla {
 namespace dom {
 
 class GlobalObject;
 class DOMMatrix;
 class DOMPoint;
-class StringOrUnrestrictedDoubleSequence;
+class StringOrUnrestrictedDoubleSequenceOrDOMMatrixReadOnly;
 struct DOMPointInit;
 struct DOMMatrixInit;
 struct DOMMatrix2DInit;
 
 class DOMMatrixReadOnly : public nsWrapperCache {
  public:
   explicit DOMMatrixReadOnly(nsISupports* aParent)
       : mParent(aParent), mMatrix2D(new gfx::MatrixDouble()) {}
@@ -78,17 +78,18 @@ class DOMMatrixReadOnly : public nsWrapp
       ErrorResult& aRv);
 
   static already_AddRefed<DOMMatrixReadOnly> FromFloat64Array(
       const GlobalObject& aGlobal, const Float64Array& aArray64,
       ErrorResult& aRv);
 
   static already_AddRefed<DOMMatrixReadOnly> Constructor(
       const GlobalObject& aGlobal,
-      const Optional<StringOrUnrestrictedDoubleSequence>& aArg,
+      const Optional<StringOrUnrestrictedDoubleSequenceOrDOMMatrixReadOnly>&
+          aArg,
       ErrorResult& aRv);
 
   static already_AddRefed<DOMMatrixReadOnly> ReadStructuredClone(
       JSContext* aCx, nsIGlobalObject* aGlobal,
       JSStructuredCloneReader* aReader);
 
   // clang-format off
 #define GetMatrixMember(entry2D, entry3D, default) \
@@ -283,32 +284,20 @@ class DOMMatrix : public DOMMatrixReadOn
   static already_AddRefed<DOMMatrix> FromFloat32Array(
       const GlobalObject& aGlobal, const Float32Array& aArray32,
       ErrorResult& aRv);
 
   static already_AddRefed<DOMMatrix> FromFloat64Array(
       const GlobalObject& aGlobal, const Float64Array& aArray64,
       ErrorResult& aRv);
 
-  static already_AddRefed<DOMMatrix> Constructor(const GlobalObject& aGlobal,
-                                                 ErrorResult& aRv);
   static already_AddRefed<DOMMatrix> Constructor(
-      const GlobalObject& aGlobal, const nsAString& aTransformList,
-      ErrorResult& aRv);
-  static already_AddRefed<DOMMatrix> Constructor(
-      const GlobalObject& aGlobal, const DOMMatrixReadOnly& aOther,
-      ErrorResult& aRv);
-  static already_AddRefed<DOMMatrix> Constructor(const GlobalObject& aGlobal,
-                                                 const Float32Array& aArray32,
-                                                 ErrorResult& aRv);
-  static already_AddRefed<DOMMatrix> Constructor(const GlobalObject& aGlobal,
-                                                 const Float64Array& aArray64,
-                                                 ErrorResult& aRv);
-  static already_AddRefed<DOMMatrix> Constructor(
-      const GlobalObject& aGlobal, const Sequence<double>& aNumberSequence,
+      const GlobalObject& aGlobal,
+      const Optional<StringOrUnrestrictedDoubleSequenceOrDOMMatrixReadOnly>&
+          aArg,
       ErrorResult& aRv);
 
   static already_AddRefed<DOMMatrix> ReadStructuredClone(
       JSContext* aCx, nsIGlobalObject* aGlobal,
       JSStructuredCloneReader* aReader);
 
   virtual JSObject* WrapObject(JSContext* aCx,
                                JS::Handle<JSObject*> aGivenProto) override;

--- a/dom/webidl/DOMMatrix.webidl
+++ b/dom/webidl/DOMMatrix.webidl
@@ -6,17 +6,17 @@
  * The origin of this IDL file is
  * https://drafts.fxtf.org/geometry/
  *
  * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
  * liability, trademark and document use rules apply.
  */
 
 [Pref="layout.css.DOMMatrix.enabled",
- Constructor(optional (DOMString or sequence<unrestricted double>) init),
+ Constructor(optional (DOMString or sequence<unrestricted double> or DOMMatrixReadOnly) init),
  Exposed=(Window,Worker),
  Serializable]
 interface DOMMatrixReadOnly {
     [NewObject, Throws] static DOMMatrixReadOnly fromMatrix(optional DOMMatrixInit other = {});
     [NewObject, Throws] static DOMMatrixReadOnly fromFloat32Array(Float32Array array32);
     [NewObject, Throws] static DOMMatrixReadOnly fromFloat64Array(Float64Array array64);
 
 
@@ -83,22 +83,17 @@ interface DOMMatrixReadOnly {
     DOMPoint                   transformPoint(optional DOMPointInit point = {});
     [Throws] Float32Array      toFloat32Array();
     [Throws] Float64Array      toFloat64Array();
     [Exposed=Window, Throws]   stringifier;
     [Default] object           toJSON();
 };
 
 [Pref="layout.css.DOMMatrix.enabled",
- Constructor,
- Constructor(DOMString transformList),
- Constructor(DOMMatrixReadOnly other),
- Constructor(Float32Array array32),
- Constructor(Float64Array array64),
- Constructor(sequence<unrestricted double> numberSequence),
+ Constructor(optional (DOMString or sequence<unrestricted double> or DOMMatrixReadOnly) init),
  Exposed=(Window,Worker),
  Serializable,
  LegacyWindowAlias=WebKitCSSMatrix]
 interface DOMMatrix : DOMMatrixReadOnly {
     [NewObject, Throws] static DOMMatrix fromMatrix(optional DOMMatrixInit other = {});
     [NewObject, Throws] static DOMMatrix fromFloat32Array(Float32Array array32);
     [NewObject, Throws] static DOMMatrix fromFloat64Array(Float64Array array64);
 

deleted file mode 100644
--- a/testing/web-platform/meta/css/geometry/DOMMatrix-001.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[DOMMatrix-001.html]
-  [new DOMMatrix(undefined)]
-    expected: FAIL