The FATCA (Foreign Account Tax Compliance Act) registration system does not support account log-in with more than one tab or window at the same time. This means that users cannot have multiple tabs or windows open simultaneously while logged into the FATCA Online Registration system. This restriction is in place to ensure the security and integrity of the system, preventing potential conflicts or errors that could arise from multiple simultaneous sessions.
Sources:
Publication 5118 (07/2021)