Dropdown Menu CSS Position

I have a website which has two separate CSS files. the main.css and nav.css. The nav.css does not work right in FireFox. The drop-down is not aligned properly. It is aligned left of the table. However, if I remove margin:0 auto; from my main.css the drop-down is then aligned properly, but then my whole website is aligned to the left instead of center.

.selectedanchor{ /*CSS class that gets added to the currently selected anchor link (assuming it's a text link)*/
background: ;
}

/* ######### Default class for drop down menus ######### */

.anylinkmenu{
position: absolute;
left: 0;
top: 0;
visibility: hidden;
border: 0px solid black;
border-bottom-width: 0;
line-height: 18px;
z-index: 100; /* zIndex should be greater than that of shadow's below */
background: #fff;
width: 200px; /* default width for menu */
}

.anylinkmenu ul{
margin: 0;
padding: 0;
list-style-type: none;
}

.anylinkmenu ul li a{
width: 100%;
display: block;
text-indent: 3px;
border-bottom: 1px solid black;
padding: 2px 0;
text-decoration: none;
text-indent: 5px;
}

.anylinkmenu a:hover{ /*hover background color*/
background: black;
color: white;

}

/* ######### Alternate multi-column class for drop down menus ######### */


.anylinkmenucols{
position: absolute;
width: 350px;
left: 0;
top: 0;
visibility: hidden;
border: 1px solid black;
padding: 10px;
z-index: 100; /*zIndex should be greater than that of shadow's below*/
background: #E9E9E9;
}

.anylinkmenucols li{
padding-bottom: 3px;
}

.anylinkmenucols .column{
float: left;
padding: 3px 8px;
margin-right: 5px;
background: #E0E0E0;
}

.anylinkmenucols .column ul{
margin: 0;
padding: 0;
list-style-type: none;
}

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