The screen shot you posted doesn't obviously match any of the listed fonts, but if you can find your OS's list of installed fonts, just check which of those you have installed.

It's kind of bizarre that you're defaulting to an italic font when the site doesn't seem to request italic, it may be that you have only the italic variant of some font installed.

Seems to be Palatino Linotype (that's the first one of the font-family my OS has available). Not sure why Opera has decided to italicise it though, as the installed font looks fine normally.

Palatino being a pre-computer font also has a tendency to be hurt by screen aliasing a lot. If you can activate some sort of anti-aliasing/smooth font layer on your computer even the italicized version shouldn't look so painful.