[xfce] Configuration of one user mixed up

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http://ubuntuforums.org – I've a problem with running an xfce session on a desktop computer. All window decorations are gone, in the settings manager I can't change the settings of the window manager (clicking on window manager gives me an empty screen, with just the return, help and close buttons). In firefox the menu's are unusable. Clicking on the menu bar gives a menu, but as soon as the cursor moves onto the menu itself it disappears most of the time (sometimes it works). In some other programs the menus work fine. Also, for a different user everything is fine and there are no problems running a unity 2D session. (Hardware)