Bring Firefox menu button back in Ubuntu

I love the Firefox menu button. But in Ubuntu it has been deactivated in favor for the global menu bar integration. If you have recently upgraded Firefox and the menu button has suddenly disappeared, here is an easy way to bring it back.

• open Firefox or just a new tab and type  about:config 
• next "promise to be careful"
• type unity in the search box and find  ui.use_unity_menubar  entry
• change it from  true  to  false 

Now the menu button is back in Firefox, but it is visible only if you choose to hide the menu bar.