'I tried it in Essential' - Note the OP is about Moodle 1.9, which has a completely different layout structure to Mdl2 and especially bootstrap themes such as Essential.
My reading of the thread currently is that the OP wanted the footer to fall below the content, and not any 'special' requirement such as frozen at the bottom of the view screen, and this would always have been the case in all the pre-existing 1.9 themes, so the issue is likely to be one of an error in the way the header.html and footer.html of the OP theme were originally constructed.
As 1.9 is no longer supported and has not been for some time, and I no longer have a copy of it on my computer anywhere, I am not really in a position to look into it in any more depth.