This file witll center the text in address bar of firefox

userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

#urlbar-container {
  text-align: center !important;
}

userContent.css

@-moz-document url-prefix(http), url-prefix(https), url-prefix(file) {
    ::selection {
        background-color: #fd6b6b !important; /* Red background */
        color: black !important; /* Black text */
        font: monospace
    }
}

@-moz-document regexp(".*\\.pdf") {
  .textLayer ::selection {
    background-color: color-mix(in srgb, #ff0000, transparent 75%) !important;
    color: transparent !important;
  }
}