When an extension is controlling the preference for "Allow pages to choose their own fonts, instead of your selections above", which is internally implemented via the "browser.display.use_document_fonts" pref, the user should be shown the extension name with an option to disable the extension. This should be similar to the cookies mocks where the options are disabled when the extension info is displayed. Mocks: https://mozilla.invisionapp.com/share/6HCITJKP8#/screens/242994351