Padding different in chrome mac vs firefox and chrome pc

Question

I'm trying to align the navigation to the banner below on the website I'm creating here: http://35.9.51.41

I've been able to make it so it aligns in Chrome and Safari on my mac, and in IE, but it is still misaligned on Firefox or any PC using Chrome or Firefox. This is making my head turn. Any suggestions?

I have a padding the determines with width of the navigation here:

#nv-tabs a {
     padding:0 33px 0 34px;
     text-decoration:none;
     cursor: pointer; /* IE 7 bug-fix */
     color:#FFFFFF!important;
     display:block;
     background:none;
     line-height: 29px; 
     z-index:100;
     font-family: Arial, sans-serif;
     text-transform:uppercase;
     font-size:13px;
     font-weight:normal;
    }

Answer 1

Define a width and it should sort your problem and also look into box-sizing: border-box