@delve I've had one sidebar reader or another installed since Firefox 1.0.
Harbi Xenu (Possibly? Name was some meaningless thing. Stopped working with Firefox 2.0)
Sage
Sage 2 (Sage didn't update so someone forked it)
Sage (Sage 2 didn't update, and Sage started updating again)
Drop Feeds (current, since Sage stopped updating)