OK, I don’t understand this at all.
This is the BBC’s RSS feed ( http://newsrss.bbc.co.uk/rss/newsonline_uk_edition/front_page/rss.xml)
If you view it in ie6 it appears to be styled with a custom stylesheet (nosol.xsl)
If you view it in firefox or ie7 the browser’s default rss feed styling is used.
I tried to do something similar myself with this rss feed: http://www.bbusl.com/worksregion/4/rss.xml
It worked as planned on the Dev server. However, once I put it live onto our production server, the ie6 stylesheet is appearing when you view the rss feed in firefox !?!
How do I make it so the custom stylesheet only appears in ie6? What’s the difference that’s made it work like that on the dev server and not the live production server?
I ran your feed through W3C’s feed validator. I configured Firefox to use Fiddler as a proxy to allow me to intercept and tinker with the response sent by your server before it was displayed by my browser.
It turns out the stylesheet is getting applied because of the first validation error:
When I changed this to the full URL for your feed the default Firefox RSS feed styling was applied as you expected to see.