More than one process is normal for the current Firefox. http://www.ghacks.net/2016/07/22/multi-process-firefox/

Multi-process Firefox is codenamed "e10s". https://wiki.mozilla.org/Firefox/multiprocess

This isn't a case of multi-processing which is what these articles address. What happens is when I click on either my desktop icon or my taskbar icon to open Firefox, the browser opens up in a window and then immediately opens up a browser in a second window so that two instances of Firefox are running at the same time. Each window has different tabs open than each other.

I should add that this only occurs after starting or restarting Windows 10. If I close Firefox and then open it back up, it only opens one instance of the browser.

Right-click that task bar icon and desktop icon and inspect the Properties > Target line to see if two URL's are in that Target line.

And also provide us with the URL's that are being loaded in each of those two browser windows, when that happens. That may give us a "tip off" as to why that is happening for you seemingly intermittently.

I don't run Win10, but use Win7, so I suspect that Win10 might be at fault when that happens after the Windows Logon User Account is being freshly loaded either by a cold start or restarting Win10.

What pages open in those Firefox windows ?

Do both open your homepage or is one blank or with a different page ?

The problem seems to have resolved itself on its own. Thanks for trying to help guys.