Mike,
A neater fix is to add the following CSS:
Here is the
Bugzilla report with all the gory details!
In short the issue only occurs when your page uses the !DOCTYPE directive, i.e. in standards mode, and the verdict is that it's not a bug but a correct, if debatable, interpretation of an ambiguous section of the CSS2 spec.
So, there you go!
Jules
P.S. Are you aware that your DOCTYPE says HTML 4.0 though you're using XHTML notation? Your DOCTYPE is also not valid for HTML 4; it should really be one of the following:
I'm aware that malformed DOCTYPEs are deliberately used in certain circumstances to fool browsers and work around certain bugs, however. Check out what the W3C has to say about
HTML Version Info if you're interested.