You got it, Rich!

Added your complete solution there to the end of that thread. :)

Having used my repaired system for several days, I regret to announce that the problem is not completely solved. While removing Link Swift did apparently improve performance, the problem has recurred. The conditions to reproduce it remain: I play a long, high-resolution Flash video (e.g. http://www.youtube.com/watch?v=kSR4xuU07sc ) with Flash Player 11,9,900,117 under Firefox 25.0 under Windows 7 Pro 64-bit Version 5.1 Build 7601). As it plays, Task Manager reports CPU load gradually increasing to 100%, at which point the video stops and the system becomes unusable. Quitting Flash Player and Firefox does not fix it. CPU load is still 100% until I reboot. If I look at Task Manager to see which tasks are taking up the CPU, it's all those tasks which shouldn't take much CPU at all, even Task Manager itself.

My easiest suggestion for you to try is to disable Flash hardware acceleration. In my opinion, this can cause very high CPU usage when watching flash videos.

To disable it, open a Youtube video and pause it. Then right-click inside the Flash video and choose "Settings". In the dialog box that opens, click the Monitor icon to see the Display settings. Last, uncheck the "Enable hardware acceleration" setting and click close. Exit Firefox and open it again to test if the problem has gone away.

If that doesn't help, you can try disabling Firefox's hardware acceleration:
Go to Firefox button > Options > Advanced > General

Then uncheck the "Use hardware acceleration when available" setting. Close Firefox for the change to take effect then open it again to see if the problem is gone.

Noah, thanks for your suggestion, but when i visited Options > Advanced > General, I found that "Use hardware acceleration when available" was already un-checked. That is to say, the setting you recommended has been in effect while all of the problems manifested.

Despite the Firefox option "Use hardware acceleration when available" being always UN-checked, when I viewed the Flash display settings per your instruction in the first half of your post, I found "Enable hardware acceleration" was checked there. I un-checked it.

I am curious, why you think that disabling hardware acceleration would prevent Flash player from burdening down my CPU even after the video is finished, as it has.

So Noah, after I disabled hardware video acceleration in both of the places you suggested:

• Firefox, Options > Advanced > General
• Flash player, settings, [monitor icon]

I returned to the YouTube video linked above, clicked the gearwheel to choose HD 720p resolution, and sat back to watch. At about 80% of the way through, CPU utilization climbed to 100% and the computer became unusable. I killed Flash and Firefox and the CPU utilization was still at 100%. I had to reboot in order to post this report.

Today's updates brought Firefox to 25.0.1 and Flash Player to 11.9.900.152. I was hoping it would make a difference in the "100% CPU" problem I had previously reported, so I returned to the YouTube video which had triggered the problem before, and played it again at the same resolution (720p). I have to say that the results are inconclusive: if forced to describe it, I would say "better but not perfect."

When the video finished playing, I re-started it. CPU usage jumped to 100% and the motion was very jerky, which led me to think the update had not fixed anything. But I was called out of the room, and when I returned a half-hour later and tried again, the video played smoothly, and other applications behaved properly, which was better than before the update (when a re-boot was required to restore normal operation). After my prior experience thinking that removing a piece of malware had fixed it, I am not willing to jump to the conclusion that the upgrade fixed it, either. Also, I discovered that the particular video linked above does not depend on flash. The 720p version is in MP4 format and plays just fine under Firefox with the Flash plug-in disabled. I'm trying to get my head around all these anecdotes to guess what the real problem is.

P.S. I checked the Firefox Release Notes and didn't recognize a reference to my specific problem, although it could have been fixed when something else was changed.

I'll post back when I know more.

Sigh. No, it's not fixed. Despite my optimistic report of yesterday, after a few more web sites, a few more videos, the CPU utilization climbed to 100% of each of my four processors, my system became unusable and had to be re-booted. It is as if Firefox gradually consumes some resource which is eventually depleted, and not restored even when Firefox quits.

Have you tried a different browser? I have reasons to suspect the problem is in the Flash player itself and is browser independent. Test also that you don't have two different versions of the flash player enabled at the same time, as it could cause conflicts.

My personal theory is that the Flash player is badly coded and creates a zombie process (which is the reason it doesn't appear on the task list). That's why the issue gets worse for each additional flash movie you play, as the zombie processes accumulate until they consume all your resources.

However, as the Flash player process is inside a DLL, you can tell your windows explorer to unload all DLLs used by an application after you exit it. You need to add a line to the windows registry: Windows XP Windows 7

This change should also speed up your windows, but it might cause trouble with a few old 16-bit applications. So it might be handy to make a backup of the registry in case you have to revert the changes.

Tell me if this solves your issue. If it doesn't, try to disable auto-update of Flash player, you can do it from your Control Panel.

Carlos, I will try your suggestions. But I should note that on my Win-XP machine I run the same versions of Firefox and Flash with no problems. So the problem is not inherent to the software, just to my installation of it.

If you think it's a trouble with your installation, I suggest to use a windows registry repair/clean tool like "Registry Cleaner", and see if that fixes your problem.

If everything else fails, check if you have conflicting codecs installed in your computer.

Carlos, I periodically I run the Quick Tune component of AVG to fix registry issues. How would I check for conflicting codecs?