Your browser is calling itselve Unknown. Now if your browser is actually Google Chrome or Opera, then they have a tendency to lie about their identity, so don't worry if this is a wrong name. Be aware that you will be treated as the browser, whose name is written here though.

And this is not just because it is tested throughly and designed primarily for running in firefox, but also because firefox on so many ways is better than most other browsers.

You actually get better quality images from this site, if you are using firefox. The page automatically detects your browser, and if it is firefox, safari, opera or chrome, you will be sent better quality png-images.
You don't seem to have a browser, which accepts high quality images. Thing is: Appareantly your browser wont do transparence onto a PNG-image that has a quality better than 255 colors or uses distortion. So the server assigns some specially crafted images for you - to make the site look somewhat ok still. This also means that you might bump into a lot of images that aren't transparent on your browser, while looking ok on others, since we can't make an alternative image for everything, just because you happen to have an outdated browser like Internet Explorer.

Not just is Internet Explorer, amongst others, unable to show transparency on high-quality PNG-images, it is also full of bugs, is slow, and generally less safe to use for surfing too. On top of that, it doesn't follow standards for rendering CSS (this is a type of code, webmasters use for changing the pages visual appearance) - which means it has a bad habit for screwing page-designs up, if people have not made an alternative CSS especially for Internet Explorer. How stupid is that?

So therefore, i urge you: Please download and install the Mozilla Firefox browser. It is free, gets updated often (and therefore is more secure and stable), and then it acts sanely on the web, opposed to Internet Explorer, which is just retarded.
Get a better webbrowsing experience, and make the life easier for web designers. Mozilla Firefox Homepage.

OK: Maybe this sounds really nerdy, but conclusion of it all is: Using Internet Explorer to view this site is kindof like watching color TV on a Black and White screen.