5000s add new about:config warning pref

user.js

@@ -1781,6 +1781,7 @@ user_pref("_user.js.parrot", "5000 syntax error: this is an ex-parrot!");
    // user_pref("full-screen-api.warning.delay", 0);
    // user_pref("full-screen-api.warning.timeout", 0);
    // user_pref("general.warnOnAboutConfig", false);
+   // user_pref("browser.aboutConfig.showWarning", false); // [FF67+]
 /* APPEARANCE ***/
    // user_pref("browser.download.autohideButton", false); // [FF57+]
    // user_pref("toolkit.cosmeticAnimations.enabled", false); // [FF55+]