Are you sure the newest version did not auto-update after install of the older one ?
What version do you have according to the following page ?
http://www.adobe.com/software/flash/about/There might be auto-update options set in control panel of Windows...

And there might be auto-update options set in your browser too...
For Firefox:

No need to go back to version v9,
version 10.1 is good until revision 53.64 included.