Yesterday I had a meeting with a client and I was late because one of my old computers (XP Pro) had slowed down way too much. All I was running was an email client (not outlook) and Firefox 3.6.8. Firefox had a been running for a few hours as I visited some websites. I couldn't bring up Task Manager or get the windows to repaint. I had to wait and wait while I tried to kill Firefox. Once I got it killed everything worked normally. This has happened several times lately - usually after visiting Facebook, then moving on elsewhere. FYI, NetScanTools is on Facebook you know.
So I did a bit of searching and found an article that explained about a new feature called plugin-container.exe. If you disable it, things appear to work better.
It's pretty simple to disable the plugin container.
Enter about:config into the browser and press Enter.
Press the scary warning button.
Look for the items beginning with dom.ipc - six will be listed, you want the middle four.
Double click on each of those four to change them from TRUE to FALSE.
At least for me the problems of memory usage and processor time disappeared. Hopefully permanently and I hope that the Firefox developers know about this and can fix it.
If you want to see the article I found, go here: