I have the same issue with my RSS extension. I have subscribed to feeds a long time ago, and never realized that these feeds has been moved to another URL because FF was able to follow the redirect. Now, FF fails at reading these feeds because it received a redirect reponse and stop there. I had to manually add code to follow the redirect.
It was working fine in FF3b4 and was broken in FF3b5.


--- On Thu, 5/8/08, Sergei Zhirikov <sfzhi@yahoo.com> wrote:
From: Sergei Zhirikov <sfzhi@yahoo.com>
Subject: FF3 fails to follow redirect when checking for extension updates
To: dev-extensions@lists.mozilla.org
Date: Thursday, May 8, 2008, 6:03 PM

Hi all,

I have moved automatic updates hosting of my extension to a new server. I
have also configured the old server to return permanent redirect (301) to
the new location for both rdf and xpi. Now if I tell Firefox 3.0b5 to check
for updates I get "An error occurred while trying to find updates for
...".From the log files on both servers I can see that FF contacts the old
server, receives redirect response, and then it does not even attempt to
follow the redirect. Both locations (the old and the new) are plain HTTP, no
SSL. The update manifest is properly signed, but that doesn't seem to be
relevant as FF doesn't even attempt to retrieve it. I'm also sure I
make a mistake in the server configuration, because FF2 finds and installs
the update without any problems. Am I dealing with a bug or is it another
security restriction introduced in Firefox 3?

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