--- a/dom/canvas/WebGL2Context.h
+++ b/dom/canvas/WebGL2Context.h
@@ -243,13 +243,14 @@ public:
 private:
 
     WebGL2Context();
 
     bool ValidateSizedInternalFormat(GLenum internalFormat, const char* info);
     bool ValidateTexStorage(GLenum target, GLsizei levels, GLenum internalformat,
                                 GLsizei width, GLsizei height, GLsizei depth,
                                 const char* info);
+    JS::Value GetTexParameterInternal(const TexTarget& target, GLenum pname) MOZ_OVERRIDE;
 };
 
 } // namespace mozilla
 
 #endif

--- a/dom/canvas/WebGL2ContextTextures.cpp
+++ b/dom/canvas/WebGL2ContextTextures.cpp
@@ -340,8 +340,22 @@ WebGL2Context::CompressedTexImage3D(GLen
 
 void
 WebGL2Context::CompressedTexSubImage3D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint zoffset,
                                        GLsizei width, GLsizei height, GLsizei depth,
                                        GLenum format, GLsizei imageSize, const dom::ArrayBufferView& data)
 {
     MOZ_CRASH("Not Implemented.");
 }
+
+JS::Value
+WebGL2Context::GetTexParameterInternal(const TexTarget& target, GLenum pname)
+{
+    switch (pname) {
+        case LOCAL_GL_TEXTURE_IMMUTABLE_FORMAT:
+        {
+            GLint i = 0;
+            gl->fGetTexParameteriv(target.get(), pname, &i);
+            return JS::NumberValue(uint32_t(i));
+        }
+    }
+    return WebGLContext::GetTexParameterInternal(target, pname);
+}

--- a/dom/canvas/WebGLContext.h
+++ b/dom/canvas/WebGLContext.h
@@ -985,16 +985,18 @@ protected:
     void UndoFakeVertexAttrib0();
 
     static CheckedUint32 GetImageSize(GLsizei height,
                                       GLsizei width,
                                       GLsizei depth,
                                       uint32_t pixelSize,
                                       uint32_t alignment);
 
+    virtual JS::Value GetTexParameterInternal(const TexTarget& target, GLenum pname);
+
     // Returns x rounded to the next highest multiple of y.
     static CheckedUint32 RoundedToNextMultipleOf(CheckedUint32 x, CheckedUint32 y) {
         return ((x + y - 1) / y) * y;
     }
 
     nsRefPtr<gl::GLContext> gl;
 
     CheckedUint32 mGeneration;

--- a/dom/canvas/WebGLContextGL.cpp
+++ b/dom/canvas/WebGLContextGL.cpp
@@ -1606,16 +1606,22 @@ WebGLContext::GetTexParameter(GLenum raw
 
     const TexTarget target(rawTarget);
 
     if (!activeBoundTextureForTarget(target)) {
         ErrorInvalidOperation("getTexParameter: no texture bound");
         return JS::NullValue();
     }
 
+    return GetTexParameterInternal(target, pname);
+}
+
+JS::Value
+WebGLContext::GetTexParameterInternal(const TexTarget& target, GLenum pname)
+{
     switch (pname) {
         case LOCAL_GL_TEXTURE_MIN_FILTER:
         case LOCAL_GL_TEXTURE_MAG_FILTER:
         case LOCAL_GL_TEXTURE_WRAP_S:
         case LOCAL_GL_TEXTURE_WRAP_T:
         {
             GLint i = 0;
             gl->fGetTexParameteriv(target.get(), pname, &i);