It seems to think it's 1998 - you know, those far-off, fabled times, when people wrote Web sites that only worked with Internet Explorer. Like this one, say, which gives the following helpful message when you view it with Firefox:
This website is best viewed on Internet Explorer version 5.3 or above
Watch out, little Post Office, I've heard a terrible rumour that the 21st century is hurtling towards you....