Comment 7 for bug 123409

I can confirm it happens with a simple script like this:

import gtk
import gtkmozembed

class TinyGecko:
    def __init__(self):
        self.moz = gtkmozembed.MozEmbed()
        self.moz.load_url('about:plugins')

        win = gtk.Window()
        win.add(self.moz)
        win.show_all()

if __name__ == '__main__':
  TinyGecko()
  gtk.main()