Connect to https://foton.szikraistvan.hu . When you first connect you will most likely receive the following warning:

Click on the Root CA and install

That's All! WOW, this was simple!
(not like in IE7 or Firefox, actually in firefox I couldn't even install the Root certificate from the chain, I had to download it manually in order to install it)
Opera Rulez!
OK, here is how you check and uninstall certificates:

Also clear and simple. I love Opera!