Have tried in both browsers, Chrome and Firefox. Makes no difference, I have also tried to select options in other drop down boxes first to see if that brings up the options but that didn't work either. I can only select the "Document Type" as a Passport and the "Year of Expiry", all other fields are blank like the month just displays "Month" and you cannot select anything else.

So I should be ok to leave the passport information blank and tell the check-in agent right?

What I also find frustrating is Etihad does not have any contact e-mails or good guidance on how to report such issues.