--- a/dom/canvas/CanvasRenderingContextHelper.cpp
+++ b/dom/canvas/CanvasRenderingContextHelper.cpp
@@ -16,16 +16,19 @@
 #include "nsDOMJSUtils.h"
 #include "nsIScriptContext.h"
 #include "nsJSUtils.h"
 #include "ClientWebGLContext.h"
 
 namespace mozilla {
 namespace dom {
 
+CanvasRenderingContextHelper::CanvasRenderingContextHelper()
+    : mCurrentContextType(CanvasContextType::NoContext) {}
+
 void CanvasRenderingContextHelper::ToBlob(
     JSContext* aCx, nsIGlobalObject* aGlobal, BlobCallback& aCallback,
     const nsAString& aType, JS::Handle<JS::Value> aParams, bool aUsePlaceholder,
     ErrorResult& aRv) {
   // Encoder callback when encoding is complete.
   class EncodeCallback : public EncodeCompleteCallback {
    public:
     EncodeCallback(nsIGlobalObject* aGlobal, BlobCallback* aCallback)

--- a/dom/canvas/CanvasRenderingContextHelper.h
+++ b/dom/canvas/CanvasRenderingContextHelper.h
@@ -32,16 +32,18 @@ enum class CanvasContextType : uint8_t {
 };
 
 /**
  * Povides common RenderingContext functionality used by both OffscreenCanvas
  * and HTMLCanvasElement.
  */
 class CanvasRenderingContextHelper {
  public:
+  CanvasRenderingContextHelper();
+
   virtual already_AddRefed<nsISupports> GetContext(
       JSContext* aCx, const nsAString& aContextId,
       JS::Handle<JS::Value> aContextOptions, ErrorResult& aRv);
 
   virtual bool GetOpaqueAttr() = 0;
 
  protected:
   virtual nsresult UpdateContext(JSContext* aCx,