userContent.css

* { font-family: sans-serif, FontAwesome, "Segoe UI Symbol", PlaceholderFontOne, "Placeholder Font Two" !important; }
pre, code { font-family: monospace !important; }
body { font-weight: 400 !important; }

@-moz-document domain("github.com") {
        .octicon, .mega-octicon {
                font-family: octicons !important;
        }

        .blob-code * {
                font-family: monospace !important;
        }

        .blob-num, .blob-code-inner {
                font-family: monospace !important;
                font-size: 13px !important;
        }

        .markdown-body {
                font-size: 13px !important;
                line-height: 1.4 !important;
        }

        .markdown-body p, li {
                margin-top: 1ex !important;
                margin-bottom: 1ex !important;
        }

        .comment-body {
                font-size: 13px !important;
        }

        .file-navigation-option .input-group .form-control {
                height: 30px !important;
        }

        .container {
                width: 1024px !important;
        }
}

@-moz-document domain("slack.com") {
        .fa {
                font-family: FontAwesome !important;
        }
}

@-moz-document domain("trello.com") {
        .icon-sm, .icon-lg {
                font-family: trellicons !important;
        }
}

@-moz-document domain("review.openstack.org") {
        .CodeMirror * {
                font-family: monospace !important;
        }

        .CodeMirror .CodeMirror-linewidget * {
                font-family: sans-serif !important;
        }
}

@-moz-document domain("etherpad.openstack.org") {
        .buttonicon {
                font-family: fontawesome-etherpad !important;
                font-size: 10px !important;
        }

        select {
                font-family: sans-serif !important;
                font-size: 10px !important;
                line-height: 10px !important;
        }

        body#innerdocbody * {
                font-family: monospace !important;
        }
}

@-moz-document domain("gog.com") {
        .ic {
                font-family: gog-icons !important;
        }
}

@-moz-document domain("docker.com") {
        body, p, li, a {
                font-weight: normal !important;
                line-height: 1.4 !important;
        }
        code {
                font-family: monospace !important;
        }
}

@-moz-document domain("wordpress.com") {
        body, input, textarea {
                font-weight: normal !important;
                line-height: 1.4 !important;
        }
        p {
                margin-bottom: 1ex !important;
        }
}

@-moz-document domain("linux.com") {
        html {
                font-weight: normal !important;
        }
}

@-moz-document domain("pagerduty.com") {
        body {
                font-weight: normal !important;
        }
}

@-moz-document domain("quip.com") {
        .icon-font {
                font-family: "Quip Glyphs" !important;
        }
}