Screenshot of it saying this?

I don't know if there is an uninstaller for Firefox on Mac that removes everything.

• https://support.mozilla.org/en-US/kb/Uninstalling+Firefox

If you want to remove profiles then you can use the Profile Manager or remove directories on the hard drive.

Firefox uses two locations for the Firefox profile folder, so remove the files in both locations. Location used for the main profile that keeps your personal data (Root Directory on about:profiles).

• ~/Library/Application Support/Firefox/Profiles/<profile>/

Location used for the disk cache and other temporary files (Local Directory on about:profiles).

• ~/Library/Caches/Firefox/Profiles/

My questions is not how to uninstall but why? Why does Firefox not create a uninstall application to remove Firefox app, history, profiles, etc.. completely?

I placed this request in feedback several years ago and since several applications include a uninstall application I don't understand why Mozilla doesn't do the same

Did you look here first. https://www.wikihow.com/Uninstall-Programs-on-Mac-Computers

As for other customs profile and addons those will not uninstall when you remove FF to get rid of those or others in the Mozilla folder you need to remove the Mozilla folder if it is showing the same in Windows. If you leave those in the same Mozilla folder without deleting it they will just reload back up.

So Firefox refuses to provide users with a Firefox complete uninstall application for some reason?

mace2 said

So Firefox refuses to provide users with a Firefox complete uninstall application for some reason?

Uninstall if only for FF itself not any customized or addons those remain. In Windows when I remove FF if - I used custom CSS the Mozilla folder will remain and only deleting it will clear any previous settings.