It sounds as if, on clicking the [more] link to bring up the pop-up with the custom smileys, you're getting a blank pop-up. Is that what you're describing? If so, and you have some add-ons for your Firefox, it may be one of them giving you trouble.
Try starting Firefox with add-ons disabled and see what happens in HAF without add-ons. Here's a guide
to that procedure. If the pop-up works in Firefox without add-ons, you can follow the directions on that page to troubleshoot the problem, or come back here for further help. To exit the add-on free Firefox, just close it, and when you restart Firefox, the add-ons will be working again. Generally, you'll want to avoid completely resetting Firefox if at all possible.