Update: I have done some further work and think I have come up with a worksable solution that sets the correct setting and also prevents the user from overriding it (easily). This is for disabling the build in PDF viewer and forcing the user to use the Adobe reader.
1. Create a userChrome.css file in your installation package in order to lock down the FrontMotion user interface and stop unwanted tinkering.
1.1. In your Front Motion Package create a file in \browser\defaults\profile\chrome called userChrome.css - This will create a customized user interface by default for your users.
1.2. Inside this file start with this code at the top:
@namespace url("
http://www.mozilla.org/keymaster/gateke ... s.only.xul"); /* set default namespace to XUL */
1.3. Add one of the following lines depending on what you want to acheive:
1.3.1. To disable ONLY the options button (the icon on the menu which is a gear) in FrontMotion use: #preferences-button { display: none !important; }
1.3.2 .To disable the full menu button (the icon with 3 lines in the top right) use: #PanelUI-menu-button { display: none !important; }
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These steps will stop the user easily getting into the options and setting the PDF action to 'save to disk', the first option I gave will still give them access to the print button, search, addons etc. The second removes the entire menu.
N.B it is still possible to get into the settings by right clicking the top of the browser and selecting Menu Bar. This will restore the old style File, Edit menu along the top of the browser. This can also be disabled in the userChrome.css if required, I opted to leave it as an option as it gives admins a way in to change things, but would take a reasonable level of knowledge and a determined effort to circumvent security by the end user to get there.
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2. Use either of the methods listed earlier in this threat to set plugin.disable_full_page_plugin_for_types to application/pdf (either by modifying the group policy template to allow it, or by adding the registry key - both of which work.
3. Do a test deployment of your new package with customized css, and this should now set the pdf reader to adobe, and stop the user from easily chaging the settings and otherwise breaking things. You can find the .css file in the user profile in Windows 7 and later in the \Users\%username%\AppData\Roaming\Mozilla\Firefox\Profiles\
random profile name\chrome folder to check that the settings have taken effect.
This has been tested with a brand new user on a test system and worked perfectly, however I am not sure how it will work with users that previously had a firefox profile. It may be worth running a GPO script to clean up old profiles from users, and then allow firefox to create a new profile with the new settings. Further investigation is required there.
Please let me know if you get stuck and I will see what I can do to help.