Why Firefox menu button disappeared?

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http://askubuntu.com – I'm using the latest stable Firefox under Ubuntu 13.04 x64. I disabled menu bar, because using the menu button is more comfortable for me. Until an update (around version 21 or 22) the button just disappeared. I checked the tool bar settings but those are correct, so nothing has been changed. I purged Firefox and removed the cache, but it is still the same. BUT I noticed an exception: if I run Firefox with sudo, the menu button appears. I'm talking about this little thing what I miss. How can I got it back permanently? (HowTos)