First of all the mac addres in a HA cluster are virtual so it'll be 1 ip per 1 virtual mac address,
During the failover the passive firewall send gratuitous arp that updates the mac table in the switches, but the mac address is the same so there's not need to clear the arp table in the layer 3 devices or your bgp peers.
Also its possible to achieve a subsecond failover in bgp active/passive if you enable graceful restart on both BGP peers,
Moving to HA A/A is a big step and will require more planning regarding session setup, session owner, distribution method...
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