Settings changed and what they do:
pref("imageblocker.enabled", true); - Enables Image Manager
pref("javascript.allow.mailnews", false); - Turns Javascript off in Mail/News
pref("browser.popupdisablingUI.enabled",true); - Enables the "Open Unrequested Windows" checkbox in Javascript prefs
pref("network.cookie.disableCookieForMailNews", true); - Disables cookies in Mail/News
pref("browser.registration.enable", false); - Disables Registration*
pref("mail.display_struct", true); - Restores the "plaintext tags" in Mail/News
pref("mailnews.message_display.allow.plugins", false); - Disables plugins in Mail/News
pref("mailnews.message_display.disable_remote_image", true); - Disables remote images in Mail/News
pref("mailnews.fakeaccount.show", false); - I guess that removes the Webmail "account"*
pref("network.http.sendRefererHeader", 1); - Don't send referrer for images (I guess this could break some porn sites? Not that I look at that stuff...)
The above prefs can be added to prefs.js or user.js by hand, except for those marked with * - they must be added to all-ns.js to function.
All in all, I'd say it works pretty much as advertised.
UserAgent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3a) Gecko/20021109