I noticed the way the rss functionality seemed to change some. Before the switch to the new software, the icons to the left of the topic name would change after you read/opened a thread. It would make it easy to distinguish new threads from older ones (at least to me ). With the newer version, the icons do not change after you have read a thread. It is something small, but it was a nice feature.
I'm using the latest version of firefox, version 3.0.11.