diff --git a/dom/canvas/WebGLContextExtensions.cpp b/dom/canvas/WebGLContextExtensions.cpp
index 74da9a0290aa..7501b1cd461a 100644
--- a/dom/canvas/WebGLContextExtensions.cpp
+++ b/dom/canvas/WebGLContextExtensions.cpp
@@ -143,8 +143,7 @@ WebGLContext::IsExtensionSupported(WebGLExtensionID ext) const
     case WebGLExtensionID::WEBGL_compressed_texture_s3tc:
         return WebGLExtensionCompressedTextureS3TC::IsSupported(this);
     case WebGLExtensionID::WEBGL_compressed_texture_s3tc_srgb:
-        return WebGLExtensionCompressedTextureS3TC::IsSupported(this) &&
-               gl->IsExtensionSupported(gl::GLContext::EXT_texture_sRGB);
+        return WebGLExtensionCompressedTextureS3TC_SRGB::IsSupported(this);
     case WebGLExtensionID::WEBGL_debug_renderer_info:
         return Preferences::GetBool("webgl.enable-debug-renderer-info", false);
     case WebGLExtensionID::WEBGL_debug_shaders:
diff --git a/dom/canvas/WebGLExtensionCompressedTextureS3TC.cpp b/dom/canvas/WebGLExtensionCompressedTextureS3TC.cpp
index 52b6edfe02b2..e032a47e99ec 100644
--- a/dom/canvas/WebGLExtensionCompressedTextureS3TC.cpp
+++ b/dom/canvas/WebGLExtensionCompressedTextureS3TC.cpp
@@ -45,13 +45,13 @@ WebGLExtensionCompressedTextureS3TC::~WebGLExtensionCompressedTextureS3TC()
 bool
 WebGLExtensionCompressedTextureS3TC::IsSupported(const WebGLContext* webgl)
 {
-   gl::GLContext* gl = webgl->GL();
-   if (gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_s3tc))
-      return true;
+    gl::GLContext* gl = webgl->GL();
+    if (gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_s3tc))
+        return true;
 
-   return gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_dxt1) &&
-          gl->IsExtensionSupported(gl::GLContext::ANGLE_texture_compression_dxt3) &&
-          gl->IsExtensionSupported(gl::GLContext::ANGLE_texture_compression_dxt5);
+    return gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_dxt1) &&
+           gl->IsExtensionSupported(gl::GLContext::ANGLE_texture_compression_dxt3) &&
+           gl->IsExtensionSupported(gl::GLContext::ANGLE_texture_compression_dxt5);
 }
 
 IMPL_WEBGL_EXTENSION_GOOP(WebGLExtensionCompressedTextureS3TC, WEBGL_compressed_texture_s3tc)
diff --git a/dom/canvas/WebGLExtensionCompressedTextureS3TC_SRGB.cpp b/dom/canvas/WebGLExtensionCompressedTextureS3TC_SRGB.cpp
index 398f19144610..c547928f4e14 100644
--- a/dom/canvas/WebGLExtensionCompressedTextureS3TC_SRGB.cpp
+++ b/dom/canvas/WebGLExtensionCompressedTextureS3TC_SRGB.cpp
@@ -42,6 +42,19 @@ WebGLExtensionCompressedTextureS3TC_SRGB::~WebGLExtensionCompressedTextureS3TC_S
 {
 }
 
+bool
+WebGLExtensionCompressedTextureS3TC_SRGB::IsSupported(const WebGLContext* webgl)
+{
+    gl::GLContext* gl = webgl->GL();
+    if (gl->IsGLES())
+        return gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_s3tc_srgb);
+
+    // Desktop GL is more complicated: It's EXT_texture_sRGB, when
+    // EXT_texture_compression_s3tc is supported, that enables srgb+s3tc.
+    return gl->IsExtensionSupported(gl::GLContext::EXT_texture_sRGB) &&
+           gl->IsExtensionSupported(gl::GLContext::EXT_texture_compression_s3tc);
+}
+
 IMPL_WEBGL_EXTENSION_GOOP(WebGLExtensionCompressedTextureS3TC_SRGB, WEBGL_compressed_texture_s3tc_srgb)
 
 } // namespace mozilla
diff --git a/dom/canvas/WebGLExtensions.h b/dom/canvas/WebGLExtensions.h
index ee10c15ccf73..7966b65f071b 100644
--- a/dom/canvas/WebGLExtensions.h
+++ b/dom/canvas/WebGLExtensions.h
@@ -138,6 +138,8 @@ public:
     explicit WebGLExtensionCompressedTextureS3TC_SRGB(WebGLContext*);
     virtual ~WebGLExtensionCompressedTextureS3TC_SRGB();
 
+    static bool IsSupported(const WebGLContext*);
+
     DECL_WEBGL_EXTENSION_GOOP
 };
 
diff --git a/gfx/gl/GLContext.cpp b/gfx/gl/GLContext.cpp
index 44f3160bdb97..f5d70e82e390 100644
--- a/gfx/gl/GLContext.cpp
+++ b/gfx/gl/GLContext.cpp
@@ -151,6 +151,7 @@ static const char* const sExtensionNames[] = {
     "GL_EXT_texture3D",
     "GL_EXT_texture_compression_dxt1",
     "GL_EXT_texture_compression_s3tc",
+    "GL_EXT_texture_compression_s3tc_srgb",
     "GL_EXT_texture_filter_anisotropic",
     "GL_EXT_texture_format_BGRA8888",
     "GL_EXT_texture_sRGB",
@@ -1739,6 +1740,13 @@ GLContext::InitExtensions()
         {
             MarkExtensionUnsupported(EXT_texture_compression_s3tc);
         }
+
+        // OSX supports EXT_texture_sRGB in Legacy contexts, but not in Core contexts.
+        // Though EXT_texture_sRGB was included into GL2.1, it *excludes* the interactions
+        // with s3tc. Strictly speaking, you must advertize support for EXT_texture_sRGB
+        // in order to allow for srgb+s3tc on desktop GL. The omission of EXT_texture_sRGB
+        // in OSX Core contexts appears to be a bug.
+        MarkExtensionSupported(EXT_texture_sRGB);
 #endif
     }
 
diff --git a/gfx/gl/GLContext.h b/gfx/gl/GLContext.h
index a469a89f3669..c4f159614479 100644
--- a/gfx/gl/GLContext.h
+++ b/gfx/gl/GLContext.h
@@ -417,6 +417,7 @@ public:
         EXT_texture3D,
         EXT_texture_compression_dxt1,
         EXT_texture_compression_s3tc,
+        EXT_texture_compression_s3tc_srgb,
         EXT_texture_filter_anisotropic,
         EXT_texture_format_BGRA8888,
         EXT_texture_sRGB,