I also have an out of box config. but I cannot assign the default vlan to irb.0
mbila@ex2300# set vlans default l3-interface irb.0
{master:0}[edit]
mbila@ex2300# commit
[edit vlans default l3-interface]
'l3-interface irb.0'
l3-interface can be configured only under vlans with 'vlan-id'/'vlan-tags'
error: commit failed: (statements constraint check failed)
{master:0}[edit]
mbila@ex2300#
mbila@ex2300> show interfaces irb terse
Interface Admin Link Proto Local Remote
irb up up
irb.0 up down inet 192.168.168.70/24