Bug 1497967 - Part 1: Add CFR opt-out string r=flod,k88hudson

Differential Revision: https://phabricator.services.mozilla.com/D9283

--HG--
extra : moz-landing-system : lando

browser/locales/en-US/browser/newtab/asrouter.ftl

@@ -13,6 +13,8 @@ cfr-doorhanger-extension-cancel-button = Not Now
 cfr-doorhanger-extension-ok-button = Add Now
   .accesskey = A
 
+cfr-doorhanger-extension-mange-settings-button = Manage Recommendation Settings
+
 cfr-doorhanger-extension-learn-more-link = Learn more
 
 # This string is used on a new line below the add-on name