If reinstalling Firefox (or your browser) and reinstalling Adobe Acrobat Reader does not work is because it is inheriting settings from past versions. What worked for me is doing a manual uninstall of all stored application data. In Win 7 Go to C:/users/your name/AppData/Roaming/Mozilla or Microsoft/ and the try to delete all of the content related to your browser including extensions and plugins. If you don't have permission to delete folders then open it and delete file by file.
Note that you have to be able to view hidden files to access AppData folder. Then do the same for the AppData under Adobe folder. Then reinstall Firefox and acrobat reader. Done!
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