I can't use anything Mozilla now on my 64-bit desktop.
Something changed in the current versions of Firefox, SeaMonkey and also Thunderbird, that on my 64-bit desktop, they all "freeze".
They would work for a while, then without warning, all activity stops. I could open a bookmark, see "Looking for
http://www.sillydog.org... and nothing happens. If I then open new tabs to retrieve the modem and router status pages using their respective IP addresses, nothing happens there either. Then anywhere between 10 seconds and one minute later, the software magically wakes up and proceeds to load in the pages on the three tabs.
Thinking that this might be hardware-related, I disabled the on-board NIC, bought a new PCI NIC, same thing occurred. I then bought a new router, same thing with the new router.
Signal levels coming from and to the cable modem were well within the normal range, so it couldn't be the modem. Plus, I did not have this problem on my 32-bit laptop (running only Ubuntu Linux).
I then installed Chromium (chromium-browser) (known as Google Chrome in the Windows world) and Claws Mail on both Windows Vista and Ubuntu Linux (64-bit). No problems with either on either operating system.

I suspect that something networking related was changed in the current versions of SM, Fx and TBird that is causing them to behave this way on that 64-bit hardware.
UserAgent: Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Ubuntu/10.10 Chromium/9.0.597.94 Chrome/9.0.597.94 Safari/534.13