This one mystifies me.
This is on my MacBook Pro. How in the world to you go from this HTML:

To this in the browser?

Look carefully at the sequence of digits for the default font.
This happens in both safari and firefox. Javascript is disabled. Disabling CSS will cause all 7s to look like 9s (because everything is then in the defaualt font).
Any clues on how to fix this would be welcome.
Several people have reported they can’t reproduce it. Here is additional information:
Mac OS 10.4.10
Firefox 2.0.0.6
Safari 3.0.3
Also, copying and pasting what looks to be “0123456979” into a text editor will give “0123456789”. Perhaps a font is corrupted so the “7” is displaying as a “9” glyph?
John Guenin suggests: Try resetting your font caches: http://www.jamapi.com/pr/fn
Thanks John. I downloaded FontNuke from the link provided and although the program itself was a bit flaky, I finally got a clean run from it and after rebooting the problem has been fixed. So the verdict is that it was probably a bad font cache that was displaying the “7” glyph incorrectly.
Whew.
Thanks to everyone who made suggestions.