There were other issues with the machine. On its own, on a good machine I've never seen this.
On my Vista Home Premium (SP1) system, I'm having what seems to be the same Firefox problem that others are complaining about, but with a twist. There are two different scenarios.
Scenario One: Firefox freezes, and when I close it, a Firefox process remains active. Therefore, trying to restart Firefox results in the message complaining that Firefox is already running. In this situation, I can open another browser program, or I can even open another Firefox instance providing I use another profile (by using the "-p -no-remote" option). Rebooting the system always resolves the problem, but only until the next "freeze up" occurs.
Scenario Two: Firefox freezes and when I close it, the Firefox process terminates. Here's the "twist" that I mentioned: In this situation, this causes my Internet connection to cease functioning, it seems. Other browsers and my e-mail program won't connect to the Internet any longer. I can't even use my browser to log-in to my router. Just as with the first scenario, rebooting the system always resolves the problem until the next freeze-up occurs.
Have other users observed this second behavior? Does this give someone a clue as to what might be happening?
One caveat ... When I close a frozen Firefox instance and the process won't terminate, this situation always interferes with my attempt to shutdown or restart the computer. The system just gets hung during the shutdown/restart process and I used to resort to doing a hard/ungraceful power switch shutdown. Naturally, I hate doing that, but I found an unconventional alternative that seems to be safer. When I know I won't be able to do a normal restart, I kill the Local Security Authority Process (lsass.exe). Windows doesn't like that and a message is displayed indicating a restart will occur after a one minute delay. This is the only graceful way I have found to restart my system in those cases when a hung Firefox process (or something) seems to be preventing a normal restart.
One more thing: I've already tried the complete de-install/removal process including complete removal of the "\Program Files\Mozilla Firefox" directory as well as removing the profile(s) in "C:\Users\<user name>\AppData\Roaming\Mozilla\Firefox\Profiles".
Any ideas? Thanks, everyone!