I sounds like Firefox security settings are working to prevent potentially malicious redirects by websites, and unless you can changes those settings, the US proxy may be your best bet.
The beginnings of our move toward OAuth 2 were fairly recent, so it's likely there are still a lot of forum posts in which we provided information about basic authentication that do not include encouragement to shift to OAuth 2. I try to encourage developers to make the move, but at present Basic Authentication is still functional and allows some initial development and concept testing before one delves into an OAuth 2 implementation. Once developers grasp the authorization and token request flows from OAuth 2, it's more simple to implement programmatically, so we believe it's a good balance of security and ease of use.
In our system, contacts (email addresses) are permanently associated with an account, once added to any list in the account, even if subsequently removed from active lists or unsubscribed from all account mailings (see this previous post, which describe our contacts data model). This allows us to enforce the wishes of your contacts if they request not to recieving your mailings, and make sure we (and you) are incompliance with anti-SPAM laws in the U.S. and other countries. In our Contact data model, lists are in turn attributes of the contact. Based on HTTP stanards, our API uses POST requests to create new contacts in an account, and PUT requests to update the details for contacts already associated with an account.
Because update requests replace current contact details with new ones provided, when you make a PUT request to update contact lists for a contact, you should include all contactlists that the contact should be on after the request is fulfilled. As such, the best flow when you need to add to the contact lists for a contact, is to get the current details for the contact, then add the additional lists to the current set of lists there, and then use the object to submit an update request for the contact.
I hope this is helfpul. Let us know if you have additional questions.
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