Mozilla is in the transition to move to a new blocklist update system based on Kinto which is more fine-grained as the old one that used a big XML document, see: https://wiki.mozilla.org/Firefox/Kinto It seems both systems are running in parallel right now but only the old one is used (see: `notify()` in `nsBlocklistService.js`) (I guess we are still in Phase 1 as outlined on the above wiki page). We should disable the one based on Kinto as there is no need to do additional requests and be affected by possible Kinto-related code issues. Flipping `services.blocklist.update_enabled` to `false` should be enough I think: ``` // If kinto update is enabled, do the kinto update if (gPref.getBoolPref(PREF_BLOCKLIST_UPDATE_ENABLED)) { const updater = Components.utils.import("resource://services-common/blocklist-updater.js", {}); updater.checkVersions().catch(() => { // Before we enable this in release, we want to collect telemetry on // failed kinto updates - see bug 1254099 }); } ```