How to set Helvetica font?

I add css:

body
{
    font-family: Helvetica, Sans-Serif;
    color: #444444;
    font-size: 9pt;
    background-color: #FAFAFA;
}

but in Mozilla I see MS shell dlg font.

Why is this happens and how will repair it? enter image description here

Update:

I set Arial but in Mozilla I see MS shell dlg again. enter image description here

Solution

If you want all browsers to use Arial whenever Helvetica is not available, you can always specify Arial as a second choice font.

body
{
    font-family: 'Helvetica', 'Arial', sans-serif;
    color: #444444;
    font-size: 9pt;
    background-color: #FAFAFA;
}

because font-family can use any number or arguments, and it will use the first one in the list that is available.