I find the problem. The problem was the gnome theme. I have the gray theme. If I change the them to Human them, all works fine...
My real problem is https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/123569
I find the problem. The problem was the gnome theme. I have the gray theme. If I change the them to Human them, all works fine...
My real problem is https:/ /bugs.launchpad .net/ubuntu/ +source/ firefox/ +bug/123569