Hi,
Since the latest update of firefox 107.0 the confirmation page does not display correctly because of a missing html tag at the beginning of the page. Firefox reports the page as being in Quirks mode because of missing
A quick fix would be nice 
If all goes well, we’ll push a new release this coming week.
I also want to emphasize and reassure everyone that this bug doesn’t break any functionality in the addon and is purely esthetic.
From https://github.com/mozilla/multi-account-containers/issues/2441#issuecomment-1321151420
Wow, Thanks for the speedy reply. I can confirm that the addon still functions correctly and this is purely an aesthetic issue.
Look forward to the update.
Cheers