Layer 2 Transparent Mode ( both in the same subnet )

Use in the case of the FW is place between machine in the same subnet ( where Zone is not need ?)

>> Layer Zone ( not Layer 3! )

>> all interface: family ethernet-switching

! Mixed-mode : l2 and L3 interface, but no IRB interface!!!

! set protocols l2-learning global-mode transparent

interface @ layer	https://community.juniper.net/communities/community-home/digestviewer/viewthread?MID=72245#bm6cc37a88-cd7c-4755-9c1b-03abc1f2dcbf
transparent-mode	put physical interfaces into zones, but you would configure them with family bridge rather than with family ethernet-switching.
ethernet-switching mode	, then you put irb interfaces into security-zones rather than physical interfaces

Mixed mode supports both transparent mode (Layer 2) and route mode (Layer 3); it's the default value.