Unable to complete card payments with Halifax Secure

Halifax use a card verification process "Halifax Secure" to verify payments made with one of their cards. Using Firefox on Linux, the pop-up window opened by to perform the verification dialogue hangs when invoked from some, but not all web sites. Turning off tracking protection for the invoking site does not solve the problem, but perhaps its redirecting to another site in the popup? Any workaround, or means of pinning down the actual cause would be appreciated. For now I'm having to switch to Chromium every time I hit this problem. Thanks.