Odd Firefox message

I've just been rebuilding my Mac and a message came up "Firefox wants to use the font "Franklin Gothic Medium" on the volume "Boot Camp.""
I've had this message before and certainly assume a rebuild would get rid of it but what is interesting now is that, while I have installed Windows XP SP2 on BootCamp, I haven't yet got around to installing Firefox on Windows!! So what is going on?

What site were you visiting when the message came up?

Can't remember. I thought it was random. Why? Do you have some knowledge about this?

This font is copyrighted and available as a purchase from Microsoft and other distributors. Used as part of Office from pre 2000:-

Franklin Gothic Medium - Version 2.20