Cannot get a Drupal feed to validate with www.feedburner.com or FireFox/yahoo reader.

The url validates at http://validator.w3.org/feed/ and it works fine with Chrome. Firefox (using Yahoo reader as default) also throws an error: "There were some problems while loading your page. We were unable to add this feed." See screenshot

I've searched hours for a solution... there are plenty others with this error too, but no solution.

The feed url is: http://musewearflipflops.com/blog/feed.xml

Can anyone see why this feed does not work with FireFox/Yahoo, or feedburner?

Thanks, Lynn Stott www.stottdesign.com