Firefox problems with Vista

My dad just got a new Compaq Presario CQ60-215DX laptop this weekend. it works well but we've run into a snag.
We installed the latest version of Firefox (3.0.6) and set it as the default browers but just after a few minutes firefox starts to not load webpages and after closing it there still is an instance of it running in task manager. We tried to close the instance in task manager but it won't close and the only way to get rid of it is by restarting the system. We also tried making IE7 the default browser but the problem still persists. Just to make sure it wasn't a network problem I used IE7 for 2 hours last night without any hiccups. While IE7 does the job my dad prefers Firefox and is wondering what the problem could be