I've been playing with this bug/infelicity for ages and I'm coming to the conclusion that it's maybe a Firefox bug in its handling of CSS.
Could any kind souls out there with nothing better to do take a look at:-
http://84-45-228-40.no-dns-yet.enta.net/twiki/bin/view/Main/WebHome
and tell me if the Search box at the top right and the text underneath it is 'off window' to the right and makes a horizontal scroll bar appear?
In IE it's perfect, everything in the right place and no horizontal scroll bar. In Firefox I get the horizontal scroll bar, the degree of the error varies according to the font size (and minimum font size) you set in preferences. I've discussed it with the author of the Twiki skin but he hasn't really been able to resolve the problem.
If anyone can check it in browsers other than IE or Firefox that would be very useful but even other versions of Firefox would be interesting.