diff --git a/dom/animation/AnimationUtils.cpp b/dom/animation/AnimationUtils.cpp
index 759de1758406..a632496625ab 100644
--- a/dom/animation/AnimationUtils.cpp
+++ b/dom/animation/AnimationUtils.cpp
@@ -10,10 +10,13 @@
 #include "nsDebug.h"
 #include "nsIAtom.h"
 #include "nsIContent.h"
+#include "nsIDocument.h"
+#include "nsGlobalWindow.h"
 #include "nsString.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/ComputedTimingFunction.h" // ComputedTimingFunction
 #include "mozilla/dom/Element.h" // For dom::Element
+#include "xpcpublic.h" // For xpc::CurrentWindowOrNull
 
 namespace mozilla {
 
@@ -99,4 +102,14 @@ AnimationUtils::ParseEasing(const dom::Element* aTarget,
   return Nothing();
 }
 
+/* static */ nsIDocument*
+AnimationUtils::GetCurrentRealmDocument(JSContext* aCx)
+{
+  nsGlobalWindow* win = xpc::CurrentWindowOrNull(aCx);
+  if (!win) {
+    return nullptr;
+  }
+  return win->GetDoc();
+}
+
 } // namespace mozilla
diff --git a/dom/animation/AnimationUtils.h b/dom/animation/AnimationUtils.h
index 3ecadb18a6dc..0c26e0ada8e7 100644
--- a/dom/animation/AnimationUtils.h
+++ b/dom/animation/AnimationUtils.h
@@ -12,6 +12,8 @@
 #include "nsStringFwd.h"
 
 class nsIContent;
+class nsIDocument;
+struct JSContext;
 
 namespace mozilla {
 
@@ -58,6 +60,12 @@ public:
    */
   static Maybe<ComputedTimingFunction>
   ParseEasing(const dom::Element* aTarget, const nsAString& aEasing);
+
+  /**
+   * Get the document from the JS context to use when parsing CSS properties.
+   */
+  static nsIDocument*
+  GetCurrentRealmDocument(JSContext* aCx);
 };
 
 } // namespace mozilla