problems in FireFox

I have 2 code lines ...in Explorer it works fine...

In firefox i have a problem some error massages...I dont know what to wrtie instead ? I mean in Firefox

the 1st line
PerentMenu is null

the 2nd line
row.childNodes in not a function

if some one can help me with this

Can you post your code or a link to the page if its online?