It turned out that the mozilla plugins folder is called "ln7gsmwv.default" on my machine. I copied libflashplayer.so from flashplayer 10 in Downloads to this folder, using the right-click menu.
These steps were taken under the advice of several members, and I thank them for getting me this far.
However, after restarting Firefox, and checking my flashplayer version at:
I still have version 9.
Do I have any remaining options?