Yes, I believe turning it off will force firefox to run all tabs in one process, which can lead to losing all your tabs if one crashes, for example.

So be warned, I guess

See also:

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

Turning off multi-process isn't advised as that will break Lockwise, but you can set the number of content processes to 1.

It is quite normal to see more Firefox processes running.

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

See also the Remote Processes section further down for more detail.

Cor-el, Thank you! All makes sense but two words are new to me: Lockwise and WebRender. Why should these matter to me? God Bless y'all for your time and knowledge.

Lockwise is the name of the Password Manager that Firefox 70 and later uses.

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-change-and-import

WebRender is the name of the component that renders websites in Firefox like the name suggests (i.e. it takes care of how you see web pages). A lot of components run in their own processor thread, so they can be restarted in can of issue instead of crashing Firefox.