How do I prevent DNS leaks on Mozilla Firefox?

Don`t need to apologize Palancar, you are right. The problem is that, sometimes, noobs like me learn more making mistakes than listening to the advices of the more experienced ones.

 

I'm surprised no one, yet, has come out with an application that uses DNSSEC to validate queries but is sent and received through SSL.

You can't be spoofed with DNSSEC and SSL keeps it private. DNS Curve or as OpenDNS called it DNSCrypt was an encryption scheme but they couldn't validate with a key because they redirect themselves at least that's my understanding anyway.

 

Palancar:

This brings an interesting question. I run DNScrypt for both my Tapi and Nic. DNScrypt encrypts DNS from the adapter back to OpenDNS servers. Aside from trust issues with OpenDNS I suspect DNScrypt plugs the Windows based DNS leaks. What is your opinion on that? Yes, I have gone about 5-6 of the DNS leak test sites.

 

The DNS addresses you set in your Network Connections > TCP/IP will override what you have in your router. So setting them in your router is kind of a extra measure more than a fail-safe.

If you chose to use Comodo Secure DNS when you install the product it will set it's DNS servers in your Network Connections, but you can change it later.

Back to the OP... the best way to prevent DNS leaks is always with firewall rules IMO. Make it so that if your internet facing apps aren't using your VPN's address/range, they won't connect at all. And do the same with svchost, OpenVPN or whatever. This way it quite simply goes through your VPN or it doesn't work period. I trust this over any tool.

Like after making a tight (allow) ruleset for those things mentioned above, like a precise source address range your VPN uses (create a zone for it if you can), and exact DNS server addresses... below them create strong Block All rules. I'm talking Block all IP In/Out. This way anything else other than what your VPN is implicitly trusted to do is flat out blocked... no exceptions. If your VPN goes down your entire internet connection goes down with the ship too, like a good Captain.