--- a/dom/media/mediasource/MediaSource.cpp
+++ b/dom/media/mediasource/MediaSource.cpp
@@ -116,18 +116,17 @@ MediaSource::IsTypeSupported(const nsASt
     if (!(Preferences::GetBool("media.mediasource.webm.enabled", false) ||
           IsWebMForced(aDiagnostics))) {
       return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
     }
     return NS_OK;
   }
   if (mimeType.EqualsASCII("audio/webm")) {
     if (!(Preferences::GetBool("media.mediasource.webm.enabled", false) ||
-          Preferences::GetBool("media.mediasource.webm.audio.enabled", true) ||
-          IsWebMForced(aDiagnostics))) {
+          Preferences::GetBool("media.mediasource.webm.audio.enabled", true))) {
       return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
     }
     return NS_OK;
   }
 
   return NS_ERROR_DOM_NOT_SUPPORTED_ERR;
 }