For anyone else struggling with this, the solution wasn't to enable "Allow Windows single sign-on for Microsoft, work, and school accounts". The issue was with cross-site cookies, which Firefox blocks by default. I was able to resolve the issue by changing the "Enhanced Tracking Protection" from "Standard" to "Custom", and setting the "Cookies" option to only block "Cookies from unvisited websites". Unchecking the "Cookies" option altogether would also work.