Why don't Firefox popups popup the correct size?

I design various popups for my own website: slingshots.com. Each popup has a length and width pixel size. In other browsers like safari, opera, aol, etc. the popups display in the correct size when they popup after clicking the link. In Firefox the right side and bottom of the popup always gets clipped so the window isn't the correct size to display the image correctly. I design the popups on a Macintosh using Leopard. I use golive and dreamweaver to create the popups. Why don't the popups show at the correct size in Firefox? Thanks Mark Ellenburg == This happened == Every time Firefox opened == I click on a popup link