try attaching the filter gradient to div#page
UPDATE
body.cbgc {
background: -moz-linear-gradient(top, rgba(125,185,232,0) 0%, rgba(30,87,153,1) 100%) no-repeat fixed;
....
}
somehow blocks the subsequent declaration of the style #page, so when you apply a filter to it, it is ignored. Try removing and filtering #pageto see if this helps.
, #page ( ), . , div, sibling #page . , , , IE.