Because Windows XP doesn't properly support a lot of the code that runs in the background, so you're missing minor elements from the page, yet it loads faster.
@KleinesSinchen As far as I know, not officially. But it's not hard to get a lot of modern programs working on XP's 64-bit version. They just don't work well. Aside from that, whatever final versions of browsers were released will likely still be somewhat functional today. I mean, I occasionally fire up my '97 Macintosh Powerbook and open Netscape Navigator to keep myself humble, and it does work on some sites.
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