You can set the number of content processes to 1.

To see more Firefox processes running is quite normal

• process for the main Firefox thread (user interface)
• one or more content processes, see:
  Options/Preferences -> General -> Performance
  remove checkmark: [ ] "Use recommended performance settings"
• process for the compositor thread
• process for extensions
• process for the WebRender when this feature is enabled

You can find the current multi-process state on the Troubleshooting Information page (about:support).

• "Help -> Troubleshooting Information"
  "Application Basics": Multiprocess Windows
  "Remote Processes" further down See also the about:memory page for information about the process IDs.

• https://support.mozilla.org/en-US/kb/performance-settings

I changed the setting to 3 and with 2 or 3 tabs open I have 6 firefox.exe running.

You can only affect the number of content processes, all other processes I mentioned above will always be present and that might be three or more processes for various parts of Firefox that each run in their own process.

firefox has always been resource hog by design albeit not intentionally initially.

"solution" is to have a bleeding edge processor with gobs of ram. With that I don't notice the generally sluggishness. this is not a solution for most people

try handicapping yourself to a single tab ever, and minimizing extensions to uBlock Origin. Never abandon adblocking.