failure to use container tabs for different AWS accounts

Hi, I was a heavy user of the multi-account containers extension. Since FF now has that functionality built in I disabled the extension recently (more than a week ago). My company keeps FF up to date - currently on 153.0.3 aarch64 All tests have been performed with other extensions (ublock origin and auto-reader view) disabled. Since the last update (last wednesday I think, 5th. Aug.) I've been unable to access the AWS or Azure portals from a container tab, though it works correctly from the 'bare' browser. I've cleared cookies and site data for the whole browser (made no difference) I've cleared cookies and site data for the container tab - this now allows me to sign into Azure (which is a prerequisite to signing into AWS), but AWS is still blocked with a microsoft message "We cannot sign you in, try a different user name" If I use the bare browser, no container, I can sign into the AWS SSO portal correctly. What can I check to help diagnose this? MacOS Tahoe 26.6.1 Firefox 153.0.3 regards Chris