--- a/netwerk/mime/nsIMIMEService.idl
+++ b/netwerk/mime/nsIMIMEService.idl
@@ -25,17 +25,17 @@ interface nsIURI;
  * acts as a general convenience wrapper of nsIMIMEInfo interfaces.
  *
  * The MIME service maintains a database with a <b>one</b> MIME type <b>to many</b>
  * file extensions rule. Adding the same file extension to multiple MIME types
  * is illegal and behavior is undefined.
  *
  * @see nsIMIMEInfo
  */
-[scriptable, uuid(5b3675a1-02db-4f8f-a560-b34736635f47)]
+[scriptable, main_process_scriptable_only, uuid(5b3675a1-02db-4f8f-a560-b34736635f47)]
 interface nsIMIMEService : nsISupports {
     /**
      * Retrieves an nsIMIMEInfo using both the extension
      * and the type of a file. The type is given preference
      * during the lookup. One of aMIMEType and aFileExt
      * can be an empty string. At least one of aMIMEType and aFileExt
      * must be nonempty.
      */