How to Fix DNS Leak in Firefox

Firefox supports DNS-over-HTTPS and proxy DNS options that may not match VPN DNS policy by default.

1. Set Firefox DNS-over-HTTPS to Off while validating VPN resolver behavior.
2. If you use SOCKS proxy, set `network.proxy.socks_remote_dns` to true in about:config.
3. Disable DNS-related add-ons that can override resolver settings.
4. Restart Firefox after VPN reconnect to ensure new network state is applied.
5. Compare quick and deep mode results to check resolver consistency.