Restore default top menu bar and bottom window bar

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http://forums.fedoraforum.org – I recently installed fedora 17 on my machine. On top menu, I wanted to add firefox short cut on top menu bar. So what I did, I dragged the Firefox menu from Application > internet > Firefox on Top menu bar beside Application and Places two default menu. but dont know what had happen, It suddenly removed both top and bottom menu bar and but firefox shortcut get added on top. Now I have only Firefox shortcut on top menu and on bottom space of bottom bar left but it doesnt show window for switching anymore. I want to get back fedora default top menu and bottom bar for window switch (HowTos)