Hi,
Am not familiar with load balancing mechanism by fit for purpose load balancers.
On the SRX, D-NAT can be used to present a "public facing" IP, similar to a floating IP.
As Steve mentions, SRXs are firewalls and not fit for purpose load balancers.
However, in routing load sharing is possible when there are 2 equal cost routes to a destination also known as ECMP.
This is enabled by applying either a load-balance per packet or per flow policy to forwarding-table or forwarding-options.
This is load-balancing in purely IP routing where there is no visibilty of application protocols and normally load shared over a core network.
Substituting an application-specific load balancer by a firewall does not guarantee the same behavior and results. However, I believe these are different technological solutions in their own rights to tackle specific challenges/problems.
Cheers,
Ashvin