"... The feed is in Atom format. It works in Safari, but not in Firefox. ..."
The reason why is you need a link tag per entry. For example:
feed
...
entry
title
id
updated
link <link href='http://foobar.com/permalink'/>
summary
content
the link bit was what I was missing so firefox goes to retrieve the link, finding it's not there fails. I just spent some time today fixing this myself.
"... Feedvalidator tells me that the date does not follow RFC-3339 ..."
I've got the same bug on my todo list. For some reason the date string format works ok but doesn't render "T" & "Z"'s. Also liked the disqus integration which I have yet to work out. Have you got any idea how much more data per post the discussion adds?
i agree, argh, but i have a few other things that i need to get out the door that i should b releasing to opensource. RegAPI stuff for SecondLife, a jQuery SettingsManager for OpenSocial, and a possible XUL extension for FF. When I get to GAE, i will post it, but for now its going to have to wait till a lull