--- a/content/canvas/src/WebGLBuffer.h
+++ b/content/canvas/src/WebGLBuffer.h
@@ -35,20 +35,20 @@ public:
     size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
         size_t sizeOfCache = mCache ? mCache->SizeOfIncludingThis(aMallocSizeOf) : 0;
         return aMallocSizeOf(this) + sizeOfCache;
     }
 
     bool HasEverBeenBound() { return mHasEverBeenBound; }
     void SetHasEverBeenBound(bool x) { mHasEverBeenBound = x; }
     GLuint GLName() const { return mGLName; }
-    GLuint ByteLength() const { return mByteLength; }
+    WebGLsizeiptr ByteLength() const { return mByteLength; }
     GLenum Target() const { return mTarget; }
 
-    void SetByteLength(GLuint byteLength) { mByteLength = byteLength; }
+    void SetByteLength(WebGLsizeiptr byteLength) { mByteLength = byteLength; }
 
     void SetTarget(GLenum target);
 
     bool ElementArrayCacheBufferData(const void* ptr, size_t buffer_size_in_bytes);
 
     void ElementArrayCacheBufferSubData(size_t pos, const void* ptr, size_t update_size_in_bytes);
 
     bool Validate(WebGLenum type, uint32_t max_allowed, size_t first, size_t count) {
@@ -64,15 +64,15 @@ public:
 
     NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(WebGLBuffer)
     NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(WebGLBuffer)
 
 protected:
 
     WebGLuint mGLName;
     bool mHasEverBeenBound;
-    GLuint mByteLength;
+    WebGLsizeiptr mByteLength;
     GLenum mTarget;
 
     nsAutoPtr<WebGLElementArrayCache> mCache;
 };
 }
 #endif //WEBGLBUFFER_H_

--- a/content/canvas/src/WebGLContextBuffers.cpp
+++ b/content/canvas/src/WebGLContextBuffers.cpp
@@ -276,17 +276,17 @@ WebGLContext::BufferSubData(GLenum targe
     if (byteOffset < 0)
         return ErrorInvalidValue("bufferSubData: negative offset");
 
     WebGLBuffer* boundBuffer = bufferSlot->get();
 
     if (!boundBuffer)
         return ErrorInvalidOperation("bufferData: no buffer bound!");
 
-    CheckedUint32 checked_neededByteLength = CheckedUint32(byteOffset) + data.Length();
+    CheckedInt<WebGLsizeiptr> checked_neededByteLength = CheckedInt<WebGLsizeiptr>(byteOffset) + data.Length();
     if (!checked_neededByteLength.isValid())
         return ErrorInvalidValue("bufferSubData: integer overflow computing the needed byte length");
 
     if (checked_neededByteLength.value() > boundBuffer->ByteLength())
         return ErrorInvalidValue("bufferSubData: not enough data - operation requires %d bytes, but buffer only has %d bytes",
                                  checked_neededByteLength.value(), boundBuffer->ByteLength());
 
     MakeContextCurrent();
@@ -312,17 +312,17 @@ WebGLContext::BufferSubData(WebGLenum ta
     if (byteOffset < 0)
         return ErrorInvalidValue("bufferSubData: negative offset");
 
     WebGLBuffer* boundBuffer = bufferSlot->get();
 
     if (!boundBuffer)
         return ErrorInvalidOperation("bufferSubData: no buffer bound!");
 
-    CheckedUint32 checked_neededByteLength = CheckedUint32(byteOffset) + data.Length();
+    CheckedInt<WebGLsizeiptr> checked_neededByteLength = CheckedInt<WebGLsizeiptr>(byteOffset) + data.Length();
     if (!checked_neededByteLength.isValid())
         return ErrorInvalidValue("bufferSubData: integer overflow computing the needed byte length");
 
     if (checked_neededByteLength.value() > boundBuffer->ByteLength())
         return ErrorInvalidValue("bufferSubData: not enough data -- operation requires %d bytes, but buffer only has %d bytes",
                                  checked_neededByteLength.value(), boundBuffer->ByteLength());
 
     boundBuffer->ElementArrayCacheBufferSubData(byteOffset, data.Data(), data.Length());