Huh? Firefox sync between devices using Firefox Browser. They are two different software companies and sync doesn't work like that AFAIK.

Huh? Firefox sync between devices using Firefox Browser.

Firefox Sync connects with a Sync server and not device to device. Most of the Firefox Sync articles here mentions the Sync server.

I would like to know how to get an "app password" for Firefox so that I can sync Outlook with Firefox. I received an error msg that said I needed to get an app password from Firefox in order to sign in to Outlook to complete the sync process. Any help would be greatly appreciated.

Firefox is a web browser while Microsoft Outlook is for email, calendars, and contacts. Perhaps you are asking about the Thunderbird email client instead.

Sorry I asked my question wrong. I need a App Password for a web based email client called GMX in order to sync MS Outlook to my email. Firefox is my primary browser

Are you using the steps in the following article, or a different method:

https://support.gmx.com/pop-imap/imap/outlook.html

For the app password, maybe this article will help -- I didn't read it in detail:

https://support.microsoft.com/en-us/account-billing/how-to-get-and-use-app-passwords-5896ed9b-4263-e681-128a-a6f2979a7944