I have found John Martin born around 1850 in the Uk census working in Liverpool . He puts his place of birth as Sligo. 
I have been searching for my John who's parents were John and Margaret in Dublin records. 
He had a sister Charlotte who was born about 1843. 
I can find no marriage for his parents or baptismal cert for Charlotte in Dublin, which has me looking outside of this area.
The John I am searching for was a tailor as is this one. I may be a long way off the mark but I am at a brick wall in Dublin. The records on IFHF do not have  a Charlotte or John born with parents John or Margaret. 
Any suggestions  Are all the records on line for Sligo through IFHF ?
much appreciate any help you can offer