MY home page header and navigator is having a space between them.

MY home page header and navigator is having a space between them in Firefox and in IE it is showing good. can anyone please give solution for this issue?

my css as follows
#header {
      
      background-image: url(../images/site/banner_gradient.gif);
      background-repeat: repeat-x;
      color: #000000;
      height: 82px;
      width: 990px;
      padding: 0;
      margin: 0;
      vertical-align: middle;      
      z-index :-1;
}