Hi Jerry, Sorry about that.

Firefox has a new multi process mode. That is intended to speed things up and increase security. It allows firefox to multi task so to speak, and it is hoped that by taking advantage of modern processors abilities Firefox gets much faster.

It is however a new complex feature and does not always work out that way. Possibly the feature does not get on well with one of the plugins you have installed. Note that you can check whether this is on or off by visiting the troubleshooting page.

• See Use the Troubleshooting Information page to help fix Firefox issues
  • Note keying in to the address bar about:support and pressing Enter is a quick method of opening that page.

Look down the left edge of the list for Multiprocess Windows if the value to the right of that starts with a zero multi process Firefox is disabled. Other wise it is on. For instance if you see 0/3 (Disabled by add-ons) that starts with a zero and multi process is off.

You will need to use about:config to turn this off by toggling the preff

browser.tabs.remote.autostart 

To false. Once you restartFirefox check again by looking at the troubleshooting page.

I gave detailed step by step instructions in

• Firefox runs in two instances in task manager
  https://support.mozilla.org/en-US/questions/1147063#answer-936259

Toggle the ...tabs.remote... prefs to false
Key in about:config press Enter key Look for the prefs that need changing. Key in on the search line bs.r wait a while for it to filter them. I see

 browser.tabs.remote.autostart 
 browser.tabs.remote.autostart.2
 browser.tabs.remote.desktopbehavior;false 

Right click each one in turn, and use the Toggle option to set each to false
Restart Firefox so the change takes place.

You should then be in ordinary Firefox without multi process.
Use about:troubleshooting to check.
The Multiprocess Windows entry should start with a zero e.g.
Multiprocess Windows 0/1 (Disabled)

Your suggestion ended the double iteration of firefox.exe. However, the single one remaining grows and grows, and eventually starts eating up 70-80% of CPU, at which point I have to exit Firefox and start all over --- again and again.

How much of the CPU resources are used depends either on what you are doing or your resources. If you have a low powered single core CPU and not proper separate graphics card and play games or HD video you will probably max out the CPU. With CPU usage growing and growing have you checked is it actually Firefox using all that CPU. Have you got other programs running in the background, maybe security AV software or Windows indexing files. Also are you getting a lot of video ads loading.

Have you seen this article

• Firefox uses too much memory or CPU resources - How to fix