MintyPhoenix

I am also having this issue on a Pixel 8 Pro immediately after installing the June security update. Clearing app cache does not help.

What’s interesting is that if you use the system back gesture (swipe from edge), the animation works as expected.

Well, not that shocked.

Check some of Firefox’s about:config flags. A number of years ago I enabled something related to Kerberos for my previous company’s (simpler) Microsoft SSO on a Mac, it may still be available and enough to work for you.