Showkase sizes gallery pages so that the gallery is displayed in full without needing to scroll vertically to see the bottom of the gallery. Showkase pages could theoretically contain a lot of content which is why the entire page is not scaled to fit within a browser window.
On a Juicebox gallery page (such as your home page), you can reduce the height of your gallery (so that your page footer is visible) by doing the following:
Edit your Juicebox gallery page
Scroll down to the 'Override Theme Settings' section
Enter a negative value (such as '-100') in the 'External fit px' text field
Click 'Update' and 'Publish'