Take a look at the Kiosk extensions available at AMO for Firefox.
https://addons.mozilla.org/en-US/firefox/search/?q=Kiosk&appver=20.0&platform=windows

There is a feature to "lock" preferences such as the home page. This article has more information: http://kb.mozillazine.org/Lock_Prefs. However, extensions can override that once they fire up, so I'm not sure how effective it will be.

Ideally every user would come to a fresh, clean, trustworthy install of Firefox. Could you use virtual machine/sandboxing technology to launch an isolated instance of Firefox that is destroyed when you exit the browser? Windows 7 Professional may include something along these lines, or perhaps a third party product could help.

You can use a mozilla.cfg file in the Firefox program folder to lock prefs or specify new (default) values.

Place a file local-settings.js in the defaults\pref folder where you also find the file channel-prefs.js to specify using mozilla.cfg.

pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0); // use this to disable the byte-shift

See:

• http://kb.mozillazine.org/Locking_preferences

These functions can be used in the mozilla.cfg file:

defaultPref();  // set new default value
pref();         // set pref, but allow changes in current session
lockPref();     // lock pref, disallow changes

You can also look at this extension:

• Public Fox: https://addons.mozilla.org/firefox/addon/public-fox/

You can hide the extension in the Add-ons manager with code in userContent.css to make it more difficult to remove or disable the extension.

• http://kb.mozillazine.org/userContent.css

Open the extension's XPI (ZIP) archive and look in the install.rdf file to see the ID (<em:id>xxx</em:id>) of that extension, GUID between curly brackets {} or an email address if that is used as ID.

@-moz-document url(about:addons){
#addons-page richlistitem[value="GUID"] { display:none!important; }
}

See also:

• http://mike.kaply.com/2012/07/03/customizing-firefox-blocking-add-ons/