Speculation:
IBKR may require third-party cookies. Such third-party cookies have been blocked by default by Firefox and Chrome for several years/months for data protection reasons.
- https://support.google.com/chrome/answer/95647?hl=en
- https://support.mozilla.org/en-US/kb/third-party-cookies-firefox-tracking-protection
(which, in my humble opinion, shows just how outdated the IBKR web interface is)