Have you checked this? ”Webpage is slowing down your browser” This is the new way the browser tells you there is a problem with the script program(s). https://support.mozilla.org/en-US/kb/warning-unresponsive-script?cache=no

https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox

Thank you, Fred. I changed it from 10 to 25. Although it reduced the number of times I get the message and the lockups are shorter, it didn't completely solve the problem. The message still appears after a couple minutes, the browser locks up for a minute or so and my CPU fan shifts to high speed.

The second links show that the foxnews.com site shows energy use often times over 100 and memory use often over 300 mb. But I knew that was the site and webpages where the problem exists.

Is this with all websites/pages, some, a few?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}