I have many email accounts for various purposes. I’ve always kept my Google container/account separate from my YouTube container/account.
With a recent update to FF I am no longer able to keep Google and YouTube separate.
Example: I open Google container and sign into 1 email address (work). Then I open youtube.com which opens in my (personal) container. Though when I attempt to login to youtube, the redirect no longer keeps me fully on youtube.com pages, with a slow page load I see a skip to my work container then an error when it lands back on the personal one.
Even with workarounds of signing in other ways, opposite directions, etc. I end up at the page https://www.youtube.com/oops
Refresh youtube.com and I am not signed in.