Comment 11 for bug 1201954

This seems to be a bug with gio handler

NS_IMETHODIMP
nsMIMEInfoUnix::GetHasDefaultHandler(bool *_retval)
{
...

  *_retval = false;
  nsRefPtr<nsMIMEInfoBase> mimeInfo = nsGNOMERegistry::GetFromType(mSchemeOrType);
<--- we check for mime type, and not for protocol handler. The older code always would fall back to protocol handler based of mailcap.

  We need to fix GetFromType(mSchemeOrType), to handle scheme ( protocol).

This is seen from here

NS_IMETHODIMP
nsGIOService::GetAppForMimeType(const nsACString& aMimeType,
                                nsIGIOMimeApp** aApp)
{
...
  GAppInfo *app_info = g_app_info_get_default_for_type(content_type, false);
...
<-- We probably need to add g_app_info_get_default_for_uri_scheme () , if app_info is null.

untested though .