RSS Feeds with Tunderbird


I am trying to use the RSS Feeds of RT 4.0 with Thunderbird. The problem
I have is that these Feeds represent different searches, i.e. New
Tickets, Tickets of User xy and so on. That is, items in the feed may
get added as well as deleted.

This is not reflected well in Thunderbird. Any item which has been
downloaded stays in the list forever, until manually deleted. It does
not refresh the feed items to match the actual contents of the feed.
This is OK for traditional newsfeeds, but does not work here.

Does anyone know how to make Thunderbird behave like I want it, perhaps
with an extension. Or can someone recommend an RSS Reader which works
this way and runs under Ubuntu?