Backing down specific (set of) packages?

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http://forums.fedoraforum.org – In particular, using the GUI, (either package kit, or yumex) I'd like to rollback Network Manager -- and if that doesn't fix the issue -- Firefox from the last series of updates. I get a little nervous using Yumex for this, in that I've never found a way to have it only downgrade specific packages. It always wants to roll-back the whole flippin' shebang. So ... am I missing something here? Is this possible (in GUI) in either yumex, or packagekit (Thusly having dependencies handled correctly)? And if so ... how? (HowTos)