I've been running GNUzilla IceCat 3.5.3 on Ubuntu 9.04 and I've noticed a weird bug with downloads. Whenever I try to open a file (or its "containing folder") from the Downloads window, I'm given a "launch application" window. I've also noticed that fonts aren't quite as smooth as compared with the corresponding version of Mozilla Firefox (this is especially noticeable with the menus and bookmarks).
~Kahlil
-- There is no system but GNU and Linux is one of its kernels.