Dr.D, i don't believe it would kill the hard. There can be a few reasons for this problem. I have heard many people with these problems. Everyones case is different, so i'm going to lay out some instances and solutions
1.If you have zonealarm uninstall it. (Zonealarm and firefox 3 cause interference problems.)
2.Try disabling active web scanning components in your anti-virus program (I don't use firefox,so i don't know if it has its own anti-virus programs or what.)
3.This one i have heard very good feedback from so try this first..
In firefox, type: "about:config" in the address bar
then, type in "ipv6" in the top filter bar
if the value = "false", right click and select "toggle".
the value now should change from "false" to "true".
4. Now, if number 3 didn't work, and the others failed then you can try resetting your router back to factory settings.
5.Also, if you have Peerguardian or peergaurdian 2 uninstall it.That messes with the connection with firefox.
Hope this helped.Give me feedback and let me know,
Blake