You don't need to log into Firefox to use it.

Are you talking about the Master Password, or website access?

I have the Firefox app on my IMac. If I quit the app or restart my Imac it asks me to log back in.

What changed?

This installation of Firefox has a new profile. A profile is the set of files where Firefox saves information such as bookmarks, passwords, and user preferences. This where I'm confused. This comes up after I quit the app or restart my IMac.

Thanks

In order to make it easier and safer to switch between installations of Firefox (including Firefox, Firefox ESR, Firefox Beta, Firefox Developer Edition, and Firefox Nightly), this installation now has a dedicated profile. It does not automatically share your saved information with other Firefox installations.

You have not lost any personal data or customizations. If you’ve already saved information to Firefox on this computer, it is still available in another Firefox installation. What are my options?

If you do nothing, your profile data in Firefox will be different from profile data in other installations of Firefox.

If you would like all of your profile data to be the same on all installations of Firefox, you can use a Firefox Account to keep them in sync.