--- a/dom/canvas/WebGLContext.cpp
+++ b/dom/canvas/WebGLContext.cpp
@@ -565,50 +565,49 @@ BaseCaps(const WebGLContextOptions& opti
 }
 
 ////////////////////////////////////////
 
 static already_AddRefed<gl::GLContext>
 CreateGLWithEGL(const gl::SurfaceCaps& caps, gl::CreateContextFlags flags,
                 WebGLContext* webgl)
 {
-    RefPtr<GLContext> gl;
-#ifndef XP_MACOSX // Mac doesn't have GLContextProviderEGL.
-    gfx::IntSize dummySize(16, 16);
-    gl = gl::GLContextProviderEGL::CreateOffscreen(dummySize, caps,
+    const gfx::IntSize dummySize(16, 16);
+    RefPtr<GLContext> gl = gl::GLContextProviderEGL::CreateOffscreen(dummySize, caps,
                                                                      flags);
+
+    if (gl && gl->IsANGLE()) {
+        gl = nullptr;
+    }
+
     if (!gl) {
         webgl->GenerateWarning("Error during EGL OpenGL init.");
         return nullptr;
     }
 
-    if (gl->IsANGLE())
-        return nullptr;
-#endif // XP_MACOSX
     return gl.forget();
 }
 
 static already_AddRefed<GLContext>
 CreateGLWithANGLE(const gl::SurfaceCaps& caps, gl::CreateContextFlags flags,
                   WebGLContext* webgl)
 {
-    RefPtr<GLContext> gl;
+    const gfx::IntSize dummySize(16, 16);
+    RefPtr<GLContext> gl = gl::GLContextProviderEGL::CreateOffscreen(dummySize, caps,
+                                                                     flags);
 
-    gfx::IntSize dummySize(16, 16);
-    gl = gl::GLContextProviderEGL::CreateOffscreen(dummySize, caps, flags);
+    if (gl && !gl->IsANGLE()) {
+        gl = nullptr;
+    }
+
     if (!gl) {
         webgl->GenerateWarning("Error during ANGLE OpenGL init.");
         return nullptr;
     }
 
-    if (!gl->IsANGLE()) {
-        MOZ_CRASH("Should only be ANGLE.");
-        return nullptr;
-    }
-
     return gl.forget();
 }
 
 static already_AddRefed<gl::GLContext>
 CreateGLWithDefault(const gl::SurfaceCaps& caps, gl::CreateContextFlags flags,
                     WebGLContext* webgl)
 {
     nsCOMPtr<nsIGfxInfo> gfxInfo = services::GetGfxInfo();
@@ -616,41 +615,42 @@ CreateGLWithDefault(const gl::SurfaceCap
     if (!(flags & CreateContextFlags::FORCE_ENABLE_HARDWARE) &&
         IsFeatureInBlacklist(gfxInfo, nsIGfxInfo::FEATURE_WEBGL_OPENGL))
     {
         webgl->GenerateWarning("Refused to create native OpenGL context because of"
                                " blacklisting.");
         return nullptr;
     }
 
-    gfx::IntSize dummySize(16, 16);
+    const gfx::IntSize dummySize(16, 16);
     RefPtr<GLContext> gl = gl::GLContextProvider::CreateOffscreen(dummySize, caps, flags);
+
+    if (gl && gl->IsANGLE()) {
+        gl = nullptr;
+    }
+
     if (!gl) {
         webgl->GenerateWarning("Error during native OpenGL init.");
         return nullptr;
     }
 
-    if (gl->IsANGLE())
-        return nullptr;
-
     return gl.forget();
 }
 
 ////////////////////////////////////////
 
 bool
 WebGLContext::CreateAndInitGLWith(FnCreateGL_T fnCreateGL,
                                   const gl::SurfaceCaps& baseCaps,
                                   gl::CreateContextFlags flags)
 {
-    MOZ_ASSERT(!gl);
-
     std::queue<gl::SurfaceCaps> fallbackCaps;
     PopulateCapFallbackQueue(baseCaps, &fallbackCaps);
 
+    MOZ_RELEASE_ASSERT(!gl);
     gl = nullptr;
     while (!fallbackCaps.empty()) {
         gl::SurfaceCaps& caps = fallbackCaps.front();
 
         gl = fnCreateGL(caps, flags, this);
         if (gl)
             break;
 
@@ -665,55 +665,39 @@ WebGLContext::CreateAndInitGLWith(FnCrea
     }
 
     return true;
 }
 
 bool
 WebGLContext::CreateAndInitGL(bool forceEnabled)
 {
-    bool preferEGL = PR_GetEnv("MOZ_WEBGL_PREFER_EGL");
+    const bool useEGL = PR_GetEnv("MOZ_WEBGL_PREFER_EGL");
+
+    bool useANGLE = false;
+#ifdef XP_WIN
+    const bool disableANGLE = (gfxPrefs::WebGLDisableANGLE() ||
+                               PR_GetEnv("MOZ_WEBGL_FORCE_OPENGL"));
+    useANGLE = !disableANGLE;
+#endif
 
     gl::CreateContextFlags flags = gl::CreateContextFlags::NONE;
     if (forceEnabled) flags |= gl::CreateContextFlags::FORCE_ENABLE_HARDWARE;
     if (!IsWebGL2())  flags |= gl::CreateContextFlags::REQUIRE_COMPAT_PROFILE;
     if (IsWebGL2())   flags |= gl::CreateContextFlags::PREFER_ES3;
 
     const gl::SurfaceCaps baseCaps = BaseCaps(mOptions, this);
 
-    MOZ_ASSERT(!gl);
-
-    if (preferEGL) {
-        if (CreateAndInitGLWith(CreateGLWithEGL, baseCaps, flags))
-            return true;
-    }
-
-    MOZ_ASSERT(!gl);
+    if (useEGL)
+        return CreateAndInitGLWith(CreateGLWithEGL, baseCaps, flags);
 
-#ifdef XP_WIN
-    const bool disableANGLE = (gfxPrefs::WebGLDisableANGLE() ||
-                               PR_GetEnv("MOZ_WEBGL_FORCE_OPENGL"));
-    if (!disableANGLE) {
-        if (CreateAndInitGLWith(CreateGLWithANGLE, baseCaps, flags))
-            return true;
+    if (useANGLE)
+        return CreateAndInitGLWith(CreateGLWithANGLE, baseCaps, flags);
 
-        // Don't fallback to WGL.
-        return false;
-    }
-#endif
-
-    MOZ_ASSERT(!gl);
-
-    if (CreateAndInitGLWith(CreateGLWithDefault, baseCaps, flags))
-        return true;
-
-    MOZ_ASSERT(!gl);
-    gl = nullptr;
-
-    return false;
+    return CreateAndInitGLWith(CreateGLWithDefault, baseCaps, flags);
 }
 
 // Fallback for resizes:
 bool
 WebGLContext::ResizeBackbuffer(uint32_t requestedWidth,
                                uint32_t requestedHeight)
 {
     uint32_t width = requestedWidth;