Open as html in firefox and chrome to see that the old sort function behaves incorrectly in firefox while the new one behaves correctly in both.

testSortByIdAndLine.html

Old output:
<div id="oldoutput">

</div>
<br /><br />
New output:
<div id="newoutput">

</div>

<script>
var vcs = [{},
{"vcID":"0_1","line":"16"},
{},
{"vcID":"2_1","line":"10"},
{},
{"vcID":"3_1","line":"19"},
{"vcID":"3_2","line":"19"},
{"vcID":"3_3","line":"19"},
{"vcID":"3_4","line":"20"},
{},
{"vcID":"4_1","line":"23"}]

function sortByIdAndLine(a, b){
    var line1 = parseInt(a.line,10);
    var line2 = parseInt(b.line,10);

    var id1 = a.vcID;
    var id2 = b.vcID;
    if(isNaN(line1) || isNaN(line2)) {
       if(isNaN(line1)) return 1;
       if(isNaN(line2)) return -1;
    }
    if(line1 < line2) return -1;
    if(line1 > line2) return 1;
    if(id1 < id2) return -1;
    if(id1 > id2) return 1;
    return 0;
}

function oldSortByIdAndLine(a, b){
    var line1 = a.line;
    var line2 = b.line;
    
    var id1 = a.vcID;
    var id2 = b.vcID;
    
    return (((typeof line1 === "undefined") || (typeof line2 === "undefined"))? 1 : (
        (line1 != line2) ? (
            (line1 < line2) ? -1 : ((line1 > line2) ? 1 : 0)
        ) : (
            (id1 < id2) ? -1 : ((id1 > id2) ? 1 : 0)
        )
        
    ));
    //return ((typeof line1 === "undefined") ? 1 : ((line1 < line2) ? -1 : ((line1 > line2) ? 1 : 0)));
}

vcs.sort(oldSortByIdAndLine);
for(var i=0;i<vcs.length;i++) {
   document.querySelector("#oldoutput").innerHTML += vcs[i].vcID + " " + vcs[i].line + "<br />\n";
}

vcs.sort(sortByIdAndLine);
for(var i=0;i<vcs.length;i++) {
   document.querySelector("#newoutput").innerHTML += vcs[i].vcID + " " + vcs[i].line + "<br />\n";
}
</script>

Ternaries ftw!

function oldSortByIdAndLine(a, b){
    var line1 = a.line;
    var line2 = b.line;

    var id1 = a.vcID;
    var id2 = b.vcID;

    return (
        !line1 || !line2 ?
            !line1 ? 1 : -1 :
                line1 < line2 ? -1 : 
                    line1 > line2 ? 1 : 
                        id1 < id2 ? -1 :
                            id1 > id2 ? 1 : 0
    );

    //return ((typeof line1 === "undefined") ? 1 : ((line1 < line2) ? -1 : ((line1 > line2) ? 1 : 0)));
}