"Courier New", Courier, monospace
should be
monospace
Specifying monospace will cause the client browser to chose the most appropriate font for monospace (often chosen by the user). Explicitly specifying a certain typeface will override the users choice.
So, the HTML/CSS output should be adjusted not to override the users' settings.
My suggestion is to update mod_dirlisting.c to generate this css instead:
a, a:active {text-decoration: none; color: blue;}
a:visited {color: #48468F;}
a:hover, a:focus {text-decoration: underline; color: red;}
h2 {margin-bottom: .6em;}
table {margin-left: .7em;}
th, td { font-family: monospace; text-align: left;}
th { font-weight: bold; padding-right: 1.2em; padding-bottom: .4em;}
td {padding-right: 1.2em;}
td.s, th.s {text-align: right;}
div.list { border-top: 1px solid #999; border-bottom: 1px solid #999; padding-top: .6em; padding-bottom: 1em;}
div.foot { font-family: monospace; font-size: 90%; color: #777; padding-top: .5em;}
That would allow for respecting user configuration, be easily printable and zoom as expected in web browsers that support it.[