/usr/lib/mozilla/plugins:
  => librhythmbox-itms-detection-plugin.so
        (size: 6088 bytes, mtime: Mon Apr  8 22:59:49 2013)
  => libgnome-shell-browser-plugin.so
        (size: 18872 bytes, mtime: Sun Mar  3 16:38:45 2013)
  => libflashplayer.so
        (size: 19232272 bytes, mtime: Thu Apr  4 11:25:10 2013)

/usr/lib/firefox/plugins: