Fire dancers, fireworks and bass-thumpin' live music ... in celebration of Conor Jr.'s christening over the weekend.

It all went down at Luttrellstown Castle in Dublin ... where McGregor, family and friends took in some serious pyro at the after-party.

Conor Sr. was all smiles for his 5-month-old ... less than 2 months after his insane payday for boxing Floyd Mayweather.

If this is all for a christening ... can you imagine this kid's 1st birthday party?!