If you're running Ubuntu 10.04 LTS with SeaMonkey 2.0.4 installed from the Ubuntu repositories, chances are that SM crashes often.
The problem is known, it's said it's because there are incompatibilities between xulrunner 1.9.1 apps and libcairo 1.8.10.
I think that the problem could be that SeaMonkey 2.0.4 is designed for xulrunner 188.8.131.52 and that xulrunner version installed on Ubuntu 10.04 is 184.108.40.206 (which is the one used by Firefox 3.6.3).
Hopefully SeaMonkey 2.0.5 which will be released very soon will use the same xulrunner version as Firefox...
Meanwhile, you can install and use SeaMonkey 2.0.4 version from Joe Lesko's PPA (we already talked about that earlier):
sudo add-apt-repository ppa:seamonkey2/seamonkey2
sudo apt-get update
sudo apt-get install seamonkey2