Unfortunately there's not a way to lock settings in Firefox at this time. There is also not a way to modify these settings via group policy or something similar.

The best solutions I can think of would be either to set the settings how you would like them and then freeze the system running Firefox, using a tool like Faronics Deep Freeze, OR run Firefox remotely (using MS RemoteApp or similar) while ensuring that the settings are set up the way you want prior to deploying the RemoteApp.

Whatever you chose to do, there is no fully internal to Firefox solution for this sort of thing.

Hi enrico8, The best place to ask is the experts on the ESR mailing list:

• https://www.mozilla.org/en-US/firefox.../faq/

However to lock this preference make sure to read the last paragraph about ESR and Adobe Acrobat in this MDN article!

• https://developer.mozilla.org/en-US/F.../Enterprise_deployment

So if I set Firefox to use Acrobat Reader to open pdf files and then in about:config page I set pdfjs.disabled to true I can obtain the wanted result?

You can only set a (default) value to prefs that are present on the about:config page.

You can't use about:config to set a choice that is stored in the mimeTypes.rdf file and "Do this automatically for files like this now on" is a setting that is stored in mimeTypes.rdf and not stored as a pref. This setting depends on the MIME type that the servers sends with a file. The built-in PDF Viewer only supports application/pdf

The mozilla.cfg file is run as a JavaScript file with chrome permissions, so in principle you could parse the mimeTypes.rdf file in the current Firefox profile folder on startup.

• http://mike.kaply.com/2012/03/22/customizing-firefox-advanced-autoconfig-files/