Having Adobe Reader XI and Acrobat Pro 9 on the same computer is a non-supported configuration. The only configuration that is supported is having the same version of Reader and Acrobat (e.g. Acrobat XI and Reader XI) installed.
I would run the repair function in Reader (in the Help menu) to see if that fixes things. If not, you may have to remove Reader, repair Acrobat and see if that lets you print again.
Firefox comes with it's own PDF viewer, and if you don't disable that, you are not using Acrobat or Reader to display and print PDF files. Are you sure you configured Firefox to use Adobe's viewer?
Karl Heinz Kremer
PDF Acrobatics Without a Net
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