User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0 Build ID: 20150319212106 Steps to reproduce: firefox 38 (downloaded as a Developer edition win64 install version) 1) opened "customization mode" 2) opened "theme^" at bottom of the screen, a menu appeared with themes Actual results: that menu appeared at the top, but mouse-over new theme "on the fly" demonstration effect was working, when i dragged cursor at bottom of the screen (just above the "theme^" i mentioned earlier) sometimes menu with different themes appears at the bottom of the screen, but at the moment, when you move the mouse cursor from one theme to another, that whole menu disappears and jumps to top of the screen, so its easy to reproduce

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Mistakenly filed against Firefox 38 and should be instead 38 Branch. Sorry for the spam. dkl