[k_sze]

That's odd. I use X on FF with not only Enhanced Tracking Protection, but also a whole bunch of other privacy extensions (uBlock Origin, Ghosterly, Disconnect.me, DuckDuckGo Privacy Essentials, EFF Privacy Badger) without adding any exception for x.com, and it still works for me.

[0dayz]

Are you logged in to your account? Since I suspect that's why.

[k_sze]

I am; but for what it's worth, if I open a new private window, I can still browse any public profile on X without logging in, and with Enhanced Tracking Protection enabled.

[0dayz]

Try doing it with removing your cookies or in a vm since it could be that Twitter uses super cookie to track you.