Firefox won't let me log in with MS Teams
Since June 2022, the Mozilla Firefox browser supports Total Cookie Protection by default. As a result, some Kanban Tool clients may experience difficulties when logging in to a Microsoft Teams-integrated account with the “Sign in with Microsoft” SSO option. The login screen may loop indefinitely, failing to complete the login action.
To solve the problem, please click on the shield icon in Firefox address bar

and disable the Enhanced Tracking Protection is ON for this site option:

That should let the page complete the login procedure.
If it did not help, please click the shield icon again, and go to Protection settings:

Under Enhanced Tracking Protection, click the Custom option and apply the Cross-site tracking cookies selection:
