The other day it was necessary to hide the “+new” button that exists in the Customer field in the Opportunity/Quote, because that button when clicked opens the windows for a new Contact.
So this is a way that can be used to hide that button:
document.getElementById("customerid_i").attributes.value = "account:true,contact:false";
Changing the “contact:true” to “contact:false”, does the work.
Hope this helps.