--- a/dom/canvas/WebGLFramebuffer.cpp
+++ b/dom/canvas/WebGLFramebuffer.cpp
@@ -404,17 +404,19 @@ WebGLFBAttachPoint::GetParameter(const c
         MOZ_ASSERT(attachment != LOCAL_GL_DEPTH_STENCIL_ATTACHMENT);
         isPNameValid = true;
         break;
 
     case LOCAL_GL_FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING:
         if (webgl->IsWebGL2() ||
             webgl->IsExtensionEnabled(WebGLExtensionID::EXT_sRGB))
         {
-            isPNameValid = true;
+            const auto format = Format()->format;
+            return JS::Int32Value(format->isSRGB ? LOCAL_GL_SRGB
+                                                 : LOCAL_GL_LINEAR);
         }
         break;
 
     ////////////////
 
     case LOCAL_GL_FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL:
         if (mTexturePtr)
             return JS::Int32Value(MipLevel());