@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain("talkingpointsmemo.com") {

h1,
    h3,
    #header ul.mainnav a,
    #header .utilities a,
    #header .utilities a.tips,
    #footer,
    .news-feature h2,
    ul.tophead li,
    h3.ads-header,
    .advertisement,
    .linklist a, .rightcol_feed a,
    div.blog h3,
    div.blog .utilities li,
    div.blog .utilities a,
    div.blog .timestamp,
    #staff,
    #story .caption,
    #story h2,
    #story .about,
    ul#latestheadlines li,
    #share,
    #share ul li a,
    .lower-election h2,
    .lower-election .byline,
    .lower-election .footer,
    .event #date-container,
    .event #desc-container .body,
    div.poll-tracker li,
    div.poll-tracker a.more-polls,
    .rightcol_feed h6,
    .lower-election .calendar-label,
    #story ul.election-calendar,
    ul.election-calendar div,
    #story ul.election-calendar div,
    #links, #masthead, #muck-blogging,
    #tagcloud,
    .muck-entry-nav,
    #comments .comment-footer,
    #profile-bar,
    #profile-bar #profile-signin label,
    .profile-input,
    .profile-input label,
    .profile-input input.text, #entry_text, .profile-input .text input,
    .profile-main h4, .profile-main h5,
    .profile-main li, .aux li,
    .profile-main .posted,
    .profile-view ul p
{
    font-family: "Helvetica Neue", Helvetica, sans-serif !important;
}

}

http://www.talkingpointsmemo.com/

This is a userstyle (for the Stylish Firefox extension) that sets the default font on Talking Points Memo to Helvetica rather than Arial.

Talking Points Memo - Prefer Helvetica

CSS