Good news on my PC issues: I have mentioned on this site that watching videos being streamed would freeze up my PC and that I needed to download videos and watch them.
Summary: it was a virus. Here's more details.
Since 1998, I have had two computers, one a Win 98 and another an XP Pro. I have had the XP Pro for about 5 years now. (I got a new XP Pro around July, and am still migrating to it; should finish the migration this month. I configured this laptop myself and believe it is close to the best one could buy in July.)
I have had 2 virus attacks to each of those computers. All 4 of those attacks were successfully resolved using the same technique. Here are the steps:
I google the symptoms. This leads me to one or two Forums dedicated to virus removal. These forums have experts in computer security from all over the world offering free step by step guidance to people with infected computers. Each topic in the forum is dedicated to one individual's issue.
(The expert for my latest case lives in Finland!)
Usually, the first thing the experts have you do is to download and run a program called "hijackthis.exe". This was created and developed by an individual (in the 90s), but is now owned by TrendMicro, and is still available for free use by anybody.
Based on the log generated by hijackthis, they have you run some virus detection tool. In my latest case, I had run both Symantec and BitDefender on my own -- neither of them detected anything wrong with the computer! But, based on the symptoms and the report by hijackthis, the expert had me run Malwarebytes Anti-Malware (mbam) product. Mbam found the Trojans. I googled the names of the files mbam found, and did not get many hits, and did not get any hits from the major security software sites such as Symantec. So it is some rare Trojan, and I am glad Malwarebytes knew about it. (There could be other viruses not known to Malwarebytes but known to Symantec or to Bitdefender! Moral: running only one security tool is not sufficient.)
The expert would then have the user direct the detection tool to remove the bad things found. In my latest case, Malwarebytes was only partially successful in getting rid of the bad things!
So then the expert had me run another tool called the "Brute Force Uninstaller" -- this one got rid of the remaining bits left un-removed by mbam.
In this HFW Forum topic, I have mentioned a memory leak seen in Firefox. The Firefox "memory leak" issue still remains and people tell me it is common. And, since the clean-up of the PC, it is not affecting my user-experience. (It could be that most of the memory leak is caused by a non-standard plugin; I'll try disabling that plugin and see what happens.)