--- a/dom/canvas/WebGLContext.cpp
+++ b/dom/canvas/WebGLContext.cpp
@@ -759,18 +759,22 @@ WebGLContext::CreateAndInitGL(bool force
             return CreateAndInitGLWith(CreateGLWithEGL, baseCaps, flags, out_failReasons);
 
         if (CreateAndInitGLWith(CreateGLWithDefault, baseCaps, flags, out_failReasons))
             return true;
     }
 
     //////
 
-    if (tryANGLE)
-        return CreateAndInitGLWith(CreateGLWithANGLE, baseCaps, flags, out_failReasons);
+    if (tryANGLE) {
+        // Force enable alpha channel to make sure ANGLE use correct framebuffer formart
+        gl::SurfaceCaps& angleCaps = const_cast<gl::SurfaceCaps&>(baseCaps);
+        angleCaps.alpha = true;
+        return CreateAndInitGLWith(CreateGLWithANGLE, angleCaps, flags, out_failReasons);
+    }
 
     //////
 
     out_failReasons->push_back(FailureReason("FEATURE_FAILURE_WEBGL_EXHAUSTED_DRIVERS",
                                              "Exhausted GL driver options."));
     return false;
 }