Making sure the domains listed in this article are allowed by your firewall or other software ensures that Firefox works correctly.
Update Service (Firefox and GMP)
Remote Settings
https://firefox.settings.services.mozilla.com https://firefox-settings-attachments.cdn.mozilla.net https://content-signature-2.cdn.mozilla.net
Download locations for Firefox
https://download.mozilla.org https://download.cdn.mozilla.net https://archive.mozilla.org https://ftp.mozilla.org
Telemetry
https://incoming.telemetry.mozilla.org
Captive Portal Detection
http://detectportal.firefox.com
Safe Browsing
https://safebrowsing.googleapis.com
https://img-getpocket.cdn.mozilla.net https://getpocket.cdn.mozilla.net
Mozilla accounts
https://accounts.firefox.com https://profile.accounts.firefox.com/
Sync
https://token.services.mozilla.com https://sync-1-us-west1-g.sync.services.mozilla.com
Tracking Protection (What exactly does it do)?
https://tracking-protection.cdn.mozilla.net
Location Services
https://location.services.mozilla.com
OpenH264 Video Codec Download
http://ciscobinary.openh264.org
Widevine Content Decryption Module Download
https://redirector.gvt1.com https://clients2.googleusercontent.com
DNS over HTTPS
https://mozilla.cloudflare-dns.com https://dns.shaw.ca https://doh.xfinity.com https://firefox.dns.nextdns.io https://private.canadianshield.cira.ca
Extension Update
https://versioncheck.addons.mozilla.org/
Extension Metadata for about:addons
https://services.addons.mozilla.org/
New Tab Sponsored Tiles
https://contile-images.services.mozilla.com