javascript - podminky

zdravim, prosim o pomoc:
mam tento js script:

var MENU_POS = [{
// item sizes
'height': 25,
'width': 144,
// menu block offset from the origin:
// for root level origin is upper left corner of the page
// for other levels origin is upper left corner of parent item
/Tohle potrebuju zapodminkovat */
'block_top': 154, //*TADYTO//
'block_left': 29, //*TADYTO//
/\*/
// offsets between items of the same level
'top': 0,
'left': 143,
...
]

Potrebuju udelat podminku pro ty dve promenne co jsem oznacim. Podminku takovouhle:
if(prohlizec=firefox)
'block_top': 154,
'block_left': 29,
elseif(prohlizec=IE)
'block_top': 154,
'block_left': 32,
endif

dikes moc za pomoc

aaa sorry uz sem to poresil..
if (window.navigator.userAgent.toLowerCase().match("gecko"))
{ }
else {
}

indexOf, match zbytecne volas regularni vyrazy pro hledani textu. Zatezujes tak prohlizec