Use the following commands to add the necessary components for IPv6 connectivity. This example was taken from an EdgeRouter X (ERX) with Spectrum Enterprise as the ISP. See comments inline.

Add the IPv6 firewall. If this is already present in the configuration, you can skip to the next section.

set firewall ipv6-name WANv6_IN default-action drop
set firewall ipv6-name WANv6_IN description 'WAN inbound traffic forwarded to LAN'
set firewall ipv6-name WANv6_IN enable-default-log
set firewall ipv6-name WANv6_IN rule 10 action accept
set firewall ipv6-name WANv6_IN rule 10 description 'Allow established/related sessions'
set firewall ipv6-name WANv6_IN rule 10 state established enable
set firewall ipv6-name WANv6_IN rule 10 state related enable
set firewall ipv6-name WANv6_IN rule 20 action drop
set firewall ipv6-name WANv6_IN rule 20 description 'Drop invalid state'
set firewall ipv6-name WANv6_IN rule 20 state invalid enable
set firewall ipv6-name WANv6_LOCAL default-action drop
set firewall ipv6-name WANv6_LOCAL description 'WAN inbound traffic to the router'
set firewall ipv6-name WANv6_LOCAL enable-default-log
set firewall ipv6-name WANv6_LOCAL rule 10 action accept
set firewall ipv6-name WANv6_LOCAL rule 10 description 'Allow established/related sessions'
set firewall ipv6-name WANv6_LOCAL rule 10 state established enable
set firewall ipv6-name WANv6_LOCAL rule 10 state related enable
set firewall ipv6-name WANv6_LOCAL rule 20 action drop
set firewall ipv6-name WANv6_LOCAL rule 20 description 'Drop invalid state'
set firewall ipv6-name WANv6_LOCAL rule 20 state invalid enable
set firewall ipv6-name WANv6_LOCAL rule 30 action accept
set firewall ipv6-name WANv6_LOCAL rule 30 description 'Allow IPv6 icmp'
set firewall ipv6-name WANv6_LOCAL rule 30 protocol ipv6-icmp
set firewall ipv6-name WANv6_LOCAL rule 40 action accept
set firewall ipv6-name WANv6_LOCAL rule 40 description 'allow dhcpv6'
set firewall ipv6-name WANv6_LOCAL rule 40 destination port 546
set firewall ipv6-name WANv6_LOCAL rule 40 protocol udp
set firewall ipv6-name WANv6_LOCAL rule 40 source port 547
set firewall ipv6-receive-redirects disable
set firewall ipv6-src-route disable

Add static address to Internet interface.

set interfaces ethernet eth0 address '26xx:e000:0:8::e:488b/127'

Add IPv6 firewall to Internet interface. This may already be present in your configuration.

set interfaces ethernet eth0 firewall in ipv6-name WANv6_IN
set interfaces ethernet eth0 firewall local ipv6-name WANv6_LOCAL

Add IPv6 connectivity to the LAN. In this case was the switch0 interface on the ERX. Change to your LAN interface. The prefix is provided by the ISP.

set interfaces switch switch0 ipv6 dup-addr-detect-transmits 1
set interfaces switch switch0 ipv6 router-advert cur-hop-limit 64
set interfaces switch switch0 ipv6 router-advert link-mtu 0
set interfaces switch switch0 ipv6 router-advert managed-flag true
set interfaces switch switch0 ipv6 router-advert max-interval 600
set interfaces switch switch0 ipv6 router-advert other-config-flag false
set interfaces switch switch0 ipv6 router-advert prefix '26xx:5c00:32e2::/64' autonomous-flag true
set interfaces switch switch0 ipv6 router-advert prefix '26xx:5c00:32e2::/64' on-link-flag true
set interfaces switch switch0 ipv6 router-advert prefix '26xx:5c00:32e2::/64' valid-lifetime 2592000
set interfaces switch switch0 ipv6 router-advert reachable-time 0
set interfaces switch switch0 ipv6 router-advert retrans-timer 0
set interfaces switch switch0 ipv6 router-advert send-advert true

Set a default IPv6 route.

set protocols static route6 '::/0' next-hop '26xx:e000:0:8::e:488a'