theme_faceted_search_ui_more uses version 5 of the l function, so the attributes should now be inside the options array.
One to watch for - this may happen elsewhere.
here is the corrected function

function theme_faceted_search_ui_more($path) {
if ($path) {
return l(t('more...'), $path, array('attributes'=>array('class' => 'faceted-search-more')));
}
else {
return ''. t('more...') .'';
}
}