Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

If we can't help, you should try asking here: https://support.microsoft.com

http://answers.microsoft.com/en-US/windows/forum/windows_10

Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

Nothing. There's no error message. It just keeps looping back to the main office.com page.

I've turned off enhanced tracking protection in all domains involved in the signin. I've created exceptions in which cookies to clear. I've tried not clearing any cookies. Tried a fresh install.

Literally nothing is working :(

I've tried not clearing any cookies

Clear the cookies.

Have you posted this on Microsoft support?

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.