Sorry to hear about the lockups. Thank you for testing a new profile. Presumably the new profile didn't/doesn't have any active extensions, except those that Firefox found in shared folders or the registry. Let's come back to that thought.

Does Windows show "not responding" in the title bar when you try to work with the frozen Firefox, or are there other signs that it's "dead"?

If you check the Windows Task Manager (Ctrl+Shift+Esc), Processes tab, how much memory is firefox.exe using when this happens? You can add a column called Commit Size or Commit Charge to the display from the View menu > Select Columns. When that gets over 2GB it can mean trouble.

Can you associate these problems with any particular websites or types of content?

Sometimes unresponsiveness can be caused by the protected mode feature of the Flash player plugin. That feature has security benefits, but seems to have serious compatibility issues on some systems. As a test, you can disable it using the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. On the right side, find "Shockwave Flash" and click the More link. Then uncheck the box for "Enable Adobe Flash protected mode" and try that for a day to see whether it helps.

I first thought maybe "virus." I ran Malwarebytes anti-malware, Microsoft Security Essentials, and scanned with my anti-virus program, AVAST. I also used Super anti-Spyware. I ran "junk removal tool" and Hijack this. I did a system restore to back two weeks prior to the problem. It ONLY locks up with Firefox. I prefer Firefox to IE or Google Chrome. When it locks up, I mean, it LOCKS up. the cursor does not move. I can not switch windows, bring up Task Manager or anything. It is completely locked. No message, no "not responding" etc. Just the same screen as when it locked up. Nothing moves!

I tried disabling flash. No help. After almost 10 minutes the computer locked. I had the task master on the screen so I could see the CPU usage at 63%. Did I mention that it locks up in safe mode as well. I saw that mentioned to someone else with this problem and I tried it. Any other ideas/suggestions?

Can you associate the high CPU/freezing with any particular websites or types of content?

Does it make any difference if you turn off the Avast Web Shield? Other users have said it makes retrieval of web pages a bit faster to not filter them, but I don't know whether it could cause lockups. Obviously you'd only test this on "safe" websites.

I disabled AVAST Web Shield and have been using Firefox for a few hours with no freezing of the computer. That must have been the problem Thank you so very much for the help.

I have this problem and I am not running Avast only Windows Defender. The only way I can get satisfaction is to unplug my modem until it stops a couple minutes later.

Hi rdwray, since you have a different configuration, could you start a new question for this problem? As always, you can use the following link, and scroll down past the suggestions if they are not relevant:

https://support.mozilla.org/questions/new/desktop/fix-problems