To manually test the message, make sure to set `browser.newtabpage.activity-stream.asrouter.devtoolsEnabled` to `true`, and then visit about:asrouter. Scroll down to the message with ID FXA_ACCOUNTS_APPMENU_PROTECT_BROWSING_DATA, and click "Show". This will default to opening the AppMenu with the message. You can open it for the PXI menu by changing `testingTriggerContext` in the test message definition from "app_menu" to "pxi_menu". Differential Revision: https://phabricator.services.mozilla.com/D224790