Bridge Mode & Modem MGMT IP & LAN IP

Hello - I'm planning on enabling bridge mode. 

Modem-->firewall-->LAN 

Questions:

what happens to the mgmt ip of the modem once in bridge mode?

How does the modem get it's IP address once in bridge mode? 

I don't want to have a dup IP and I want to be able to get back into the modem just in case something goes wrong and I need to disable bridge mode because my firewall LAN will be configure with the same IP.  

Looking for other folks that have done this and don't mind sharing their experienced.  

Thanks in advance.