It appears that Google, owners of reCaptcha have changed their code and it broke Firefox - on purpose or by accident, it's too early to decide! I can still pass reCaptcha by using the Chrome browser so maybe that what the Goog wants.
A workaround seems to be changing the UserAgent string in Firefox to mimic Chrome. I installed the User-Agent Switcher by Erin Schlarb as a temporary fix and it's working fine for me. I chose the Windows Chrome 123 option in the dropdown.
When it gets a proper fix I can simply remove the add-on.