OK, so I upgraded to Adobe’s latest version of the Flash plugin recently, version 10.

Big mistake.

My Intel Mac desktop machine promptly started getting very cranky. Safari slowed down. Video playback was jerky and slow. Other applications were affected too; the excellent utility Keyboard Maestro became almost unuseable, it was so sluggish.

By tracking back to what I’d changed recently, I started to suspect the Flash 10 plugin. So here’s what I did to fix the problem:

1) I used the Adobe Flash uninstaller to remove all traces of version 10. (Beware: on my system, this took more than an hour to execute.)

2) When that was finally done, I ran the Apple Disk Utility program to repair permissions on my startup disk, because I always do that after operations that modify system files. (Regularly repairing permissions is a simple way to avoid problems with any Mac OS installation.)

3) I downloaded version 9 of the Flash plugin from this page, and installed the correct version according to the readme.txt file in the ZIP archive. (For my Intel system, it was flashplayer9r159_ub_mac.dmg.zip.)

After all of these machinations, my system’s pipes are clean again, videos are running smoothly, and the other applications that were sluggish are now quick as bunnies.

Flash 10. Just don’t do it.