Steps to replicate the issue (include links if applicable):

• In a fresh OS and browser I logged in to en.wikipedia.org. Once the form was accepted, the page loaded as if I was logged out (with 'Donations Preferences Create account Log in' at top right)
• Clicking on 'Log in' refreshed the page and showed me as logged in (with my username, alerts etc)
• When I visited commons.wikimedia.org, and then en.wiktionary.org the same behaviour existed.
• Note 1: this was after a password reset, not sure if that matters. T130015 may be related, but my login was successful - it was just not displaying.
• Note 2: I did a quick search on Phabricator but I may have missed a duplicate task - they are a bit too technically worded for me.

What should have happened instead?:

• Once you have logged in, the page (and any subsequent Wikimedia page) should should you as logged in.

Other information (browser name/version, screenshots, etc.):
Firefox 143.0.3 / Firefox for Fedora. Regular browsing session (not private), I have uBlock Origin installed, but otherwise a pretty much a clean install.