No problem with Windows 10 and logging into the firefox forum help sections. I think your phone saved the login but your computer didn't save so you need to go back to check your login and password.

MaxxSound said

My Firefox login account works from Android, does not work from Windows 10 desktop. error: "Please enter a correct username and password. Note that both fields are case-sensitive." Is there a possible browser setting that needs to be checked?

An account on what site or service?

Are you talking about your account on this https://support.mozilla.org site or are you talking about a Firefox Account in which this site does not make use of.

https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-account