Why thank you
As I read down the page on the Spread Firefox website I wasn't sure if there was going to be anything I could do - but they seem to be happy with any contributions at all, even if it's just copying and pasting code to create an email sig or webpage link.
I had to modify the page link code to make it work as my forum sig as we can't put HTML in our sigs here, but if anyone wants to add the one I'm using to their CF sig, the code is:
[ URL=http://spreadfirefox.com/community/?q=affiliates&id=0&t=55"][ img]http://www.spreadfirefox.com/community/images/affiliates/Buttons/180x60/trust.gif[/IMG][/URL]
... with the spaces removed from the URL and IMG tags.
The site has other images to choose from as well.