--- a/content/canvas/src/WebGLContextGL.cpp
+++ b/content/canvas/src/WebGLContextGL.cpp
@@ -3928,18 +3928,16 @@ WebGLContext::ReadPixels(WebGLint x, Web
     }
 
     MakeContextCurrent();
 
     if (mBoundFramebuffer) {
         // prevent readback of arbitrary video memory through uninitialized renderbuffers!
         if (!mBoundFramebuffer->CheckAndInitializeRenderbuffers())
             return ErrorInvalidFramebufferOperation("readPixels: incomplete framebuffer");
-    } else {
-        EnsureBackbufferClearedAsNeeded();
     }
     // Now that the errors are out of the way, on to actually reading
 
     // If we won't be reading any pixels anyways, just skip the actual reading
     if (width == 0 || height == 0)
         return DummyFramebufferOperation("readPixels");
 
     if (CanvasUtils::CheckSaneSubrectSize(x, y, width, height, framebufferWidth, framebufferHeight)) {