Happily I appear to have fixed the issue with footer styling as detailed in my last post. Oh to have such an easy answer to all my problems!
The addition of
{display:block;}
to the css told the browser (in this case firefox 3.0.6) what sort of element <footer> is and therefore how it should be dealt with.
Result – display as originally expected:
Big thanks to Bruce and David for pointing out this simple but effective solution.