This may not be the cause in your case, but there have been examples where the pages have not been given a 'DOCTYPE' declaration at the beginning of the html. If this (or something similar):
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en">
is not at the top of your page, then some browsers (Mozilla) will display the buttons while others (some IE) won't.