Bug 1616347 - Add a preference to control caching about:home. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D64188

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

browser/app/profile/firefox.js

@@ -222,6 +222,8 @@ pref("browser.defaultbrowser.notificationbar", false);
 // The behavior of option 3 is detailed at: http://wiki.mozilla.org/Session_Restore
 pref("browser.startup.page",                1);
 pref("browser.startup.homepage",            "about:home");
+pref("browser.startup.homepage.abouthome_cache.enabled", false);
+
 // Whether we should skip the homepage when opening the first-run page
 pref("browser.startup.firstrunSkipsHomepage", true);