Must... not... get... angry...
There's enough security problems with Spanish government websites to give security researchers work for a lifetime. They seem to still think it's acceptable that their websites work on IE6 on XP and everyone else can get knotted. There are still government websites out there that manage to use both ActiveX and Java.
It's the FNMT (their equivalent of the Royal Mint or US Mint) that issues Spanish certificates, yet they're not really set up as a CA. They've been trying to get CA status for Firefox for 7 years...
https://bugzilla.mozilla.org/show_bug.cgi?id=435736
This means you have to mess about installing root certificates and maybe certificates specific to the government website you're visiting *. This is the problem mentioned in the article.
Another thing, in Firefox you have to tone down the security to make things work (signed.applets.codebase_principal_support in about:config).
Every time the tax return comes round some horrible Java abortion which doesn't work is foisted on the populace and the website is unable to cope with the load. You either have to scour Internet forums to find out what version of Java and browser you have to roll back to so it does work or go and see them personally, which is what online stuff is supposed to avoid.
And when Oracle makes Java's security policies stricter everything stops working for months too. Hey, how about following best practice from the beginning?
This is what happens when big consultancies in with the government pocket the cash and then give the work to new graduates which are cheap.
Rant over.
* Yes, you have to download the certificates insecurely.