--- a/services/settings/RemoteSettingsClient.sys.mjs
+++ b/services/settings/RemoteSettingsClient.sys.mjs
@@ -621,6 +621,8 @@
    * @param {Object} options See #maybeSync() options.
    */
   async sync(options) {
+    return; /* Hard-disable sync */
+
     if (lazy.Utils.shouldSkipRemoteActivityDueToTests) {
       return;
     }
--- a/services/settings/remote-settings.sys.mjs
+++ b/services/settings/remote-settings.sys.mjs
@@ -209,6 +209,8 @@
    * @throws {Error} If the signature of any bundled changeset is invalid.
    */
   remoteSettings.pullStartupBundle = async () => {
+    return [];  /* Hard-disable pulling it */
+
     if (lazy.Utils.shouldSkipRemoteActivityDueToTests) {
       return [];
     }
@@ -304,6 +306,8 @@
     trigger = "manual",
     full = false,
   } = {}) => {
+    return; /* Hard-disable polling remote settings */
+
     if (lazy.Utils.shouldSkipRemoteActivityDueToTests) {
       return;
     }