Browser repainting graphics

I wonder if anyone else has encountered this problem… i have an index page with a header and a content div, the content div is basically empty but for a php if which includes() the relevant page. The relevant page then is contained within its own div which puts a border etc on. So then all links call index but with a different variable. After the content is a footer.

However on some pages when you first visit them the content area isn’t “pushing down” the footer… so in essence part of it is hidden. If you refresh the browser or even just refresh the graphics drawn out by resizing the window, then it all shunts down and fits properly…

has anyone else ever had this?? if so, is there a solution?? (im viewing in firefox btw)