--- a/dom/canvas/WebGLTextureUpload.cpp
+++ b/dom/canvas/WebGLTextureUpload.cpp
@@ -1722,22 +1722,25 @@ ValidateCopyTexImageFormats(WebGLContext
 
 ////////////////////////////////////////////////////////////////////////////////
 
 class ScopedCopyTexImageSource
 {
     WebGLContext* const mWebGL;
     GLuint mRB;
     GLuint mFB;
+    GLenum mSrcSizedFormat;
 
 public:
     ScopedCopyTexImageSource(WebGLContext* webgl, const char* funcName, uint32_t srcWidth,
                              uint32_t srcHeight, const webgl::FormatInfo* srcFormat,
                              const webgl::FormatUsageInfo* dstUsage);
     ~ScopedCopyTexImageSource();
+    bool IsValidFB() { return mFB != 0;}
+    GLenum GetSourceSizedFormat() {return mSrcSizedFormat;}
 };
 
 ScopedCopyTexImageSource::ScopedCopyTexImageSource(WebGLContext* webgl,
                                                    const char* funcName,
                                                    uint32_t srcWidth, uint32_t srcHeight,
                                                    const webgl::FormatInfo* srcFormat,
                                                    const webgl::FormatUsageInfo* dstUsage)
     : mWebGL(webgl)
@@ -1759,31 +1762,29 @@ ScopedCopyTexImageSource::ScopedCopyTexI
         return;
     }
 
     if (!dstUsage->textureSwizzleRGBA)
         return;
 
     gl::GLContext* gl = webgl->gl;
 
-    GLenum sizedFormat;
-
     switch (srcFormat->componentType) {
     case webgl::ComponentType::NormUInt:
-        sizedFormat = LOCAL_GL_RGBA8;
+        mSrcSizedFormat = LOCAL_GL_RGBA8;
         break;
 
     case webgl::ComponentType::Float:
         if (webgl->IsExtensionEnabled(WebGLExtensionID::WEBGL_color_buffer_float)) {
-            sizedFormat = LOCAL_GL_RGBA32F;
+            mSrcSizedFormat = LOCAL_GL_RGBA32F;
             break;
         }
 
         if (webgl->IsExtensionEnabled(WebGLExtensionID::EXT_color_buffer_half_float)) {
-            sizedFormat = LOCAL_GL_RGBA16F;
+            mSrcSizedFormat = LOCAL_GL_RGBA16F;
             break;
         }
         MOZ_CRASH("GFX: Should be able to request CopyTexImage from Float.");
 
     default:
         MOZ_CRASH("GFX: Should be able to request CopyTexImage from this type.");
     }
 
@@ -1812,25 +1813,25 @@ ScopedCopyTexImageSource::ScopedCopyTexI
         MOZ_CRASH("GFX: Unhandled unsizedFormat.");
     }
 
     gl->fTexParameteri(LOCAL_GL_TEXTURE_2D, LOCAL_GL_TEXTURE_SWIZZLE_R, blitSwizzle[0]);
     gl->fTexParameteri(LOCAL_GL_TEXTURE_2D, LOCAL_GL_TEXTURE_SWIZZLE_G, blitSwizzle[1]);
     gl->fTexParameteri(LOCAL_GL_TEXTURE_2D, LOCAL_GL_TEXTURE_SWIZZLE_B, blitSwizzle[2]);
     gl->fTexParameteri(LOCAL_GL_TEXTURE_2D, LOCAL_GL_TEXTURE_SWIZZLE_A, blitSwizzle[3]);
 
-    gl->fCopyTexImage2D(LOCAL_GL_TEXTURE_2D, 0, sizedFormat, 0, 0, srcWidth,
+    gl->fCopyTexImage2D(LOCAL_GL_TEXTURE_2D, 0, mSrcSizedFormat, 0, 0, srcWidth,
                         srcHeight, 0);
 
     // Now create the swizzled FB we'll be exposing.
 
     GLuint rgbaRB = 0;
     gl->fGenRenderbuffers(1, &rgbaRB);
     gl::ScopedBindRenderbuffer scopedRB(gl, rgbaRB);
-    gl->fRenderbufferStorage(LOCAL_GL_RENDERBUFFER, sizedFormat, srcWidth, srcHeight);
+    gl->fRenderbufferStorage(LOCAL_GL_RENDERBUFFER, mSrcSizedFormat, srcWidth, srcHeight);
 
     GLuint rgbaFB = 0;
     gl->fGenFramebuffers(1, &rgbaFB);
     gl->fBindFramebuffer(LOCAL_GL_FRAMEBUFFER, rgbaFB);
     gl->fFramebufferRenderbuffer(LOCAL_GL_FRAMEBUFFER, LOCAL_GL_COLOR_ATTACHMENT0,
                                  LOCAL_GL_RENDERBUFFER, rgbaRB);
 
     const GLenum status = gl->fCheckFramebufferStatus(LOCAL_GL_FRAMEBUFFER);
@@ -2068,17 +2069,19 @@ WebGLTexture::CopyTexImage2D(TexImageTar
     uint32_t readX, readY;
     uint32_t writeX, writeY;
     uint32_t rwWidth, rwHeight;
     Intersect(srcWidth, x, width, &readX, &writeX, &rwWidth);
     Intersect(srcHeight, y, height, &readY, &writeY, &rwHeight);
 
     GLenum error;
     if (rwWidth == uint32_t(width) && rwHeight == uint32_t(height)) {
-        error = DoCopyTexImage2D(gl, target, level, internalFormat, x, y, width, height);
+        GLenum validFormat = maybeSwizzle.IsValidFB() ?
+            maybeSwizzle.GetSourceSizedFormat() : internalFormat;
+        error = DoCopyTexImage2D(gl, target, level, validFormat, x, y, width, height);
     } else {
         // 1. Zero the texture data.
         // 2. CopyTexSubImage the subrect.
 
         const bool respecifyTexture = true;
         const uint8_t zOffset = 0;
         if (!ZeroTextureData(mContext, funcName, respecifyTexture, mGLName, target, level,
                              dstUsage, 0, 0, zOffset, width, height, depth))