Had identical problem, this fixed it.
If problems arise or if you want to restore the default set of file download actions, do the following [8]:
Type about:config into the address bar.
Find the preference browser.download.pluginOverrideTypes and, if it is present, right-click on it and select reset.
Find the preference plugin.disable_full_page_plugin_for_types and, if it is present, right-click on it and select reset.
Open the profile folder. (The profile folder is hidden by default in Windows 7/Vista/XP/2000 and Linux; read this for help finding it).
Note: In Firefox 3.6 and above you can open the profile folder from the Firefox menu, via "Help -> Troubleshooting Information".
Completely close your Mozilla browser.
Delete (or rename) the file mimeTypes.rdf. Caution: There is also a mimeTypes.rdf file in the program folder. Do not delete it by mistake.