Looking in the dictionary, I see liberal as "willing to respect or accept behaviour or opinions different from one's own", which is what I (as a European) had always thought -- what does it mean in America?

Politically left-wing.

Increasingly these days, it seems to be a term for anyone who doesn't give credence to the theory that global warming is a hoax made up by Satan so Barack Obama can marry his secret Kenyan gay lover.

It means "leftist" AFAIK

They said they're both European

I guess both are liberal in the US sense of term but are not agreeing about if they have to mandatory delete the contents or to mandatory do the reverse. :)

Sure, but Europeans are quite capable of using a term differently if they believe that's what their audience expects; and most people on HN are probably still USA-ian ;-)

Thats precisely the point ;).