message: Show Firefox mis-support only in Firefox' options
diff: textarea {
  width: 100%;
  }
  + .only-firefox {
  + display: none;
  + }
  + @-moz-document url-prefix() {
  + .no-firefox {
  + display: none;
  + }
  + .only-firefox {
  + display: block;
  + }
  + }
  </style>
  <form id="options-form">
  <h2>GitHub Enterprise</h2>
  - <p>
  - While on your GitHub, right-click on Refined GitHub's icon in the toolbar and select <strong>Enable Refined GitHub on this domain</strong>.
  - <a href="https://user-images.githubusercontent.com/1402241/32874388-e0c64150-cacc-11e7-9a50-eae3727fd3c2.png" target="_blank">Example</a>. This is <a href="https://github.com/sindresorhus/refined-github/issues/840#issuecomment-349936195" target="_blank">not yet supported by Firefox</a>.
  + <p class="no-firefox">
  + Visit your GH Enterprise, right-click on <a href="https://user-images.githubusercontent.com/1402241/32874388-e0c64150-cacc-11e7-9a50-eae3727fd3c2.png" target="_blank">Refined GitHub's icon in the toolbar</a> and select <strong>Enable Refined GitHub on this domain</strong>.
  + </p>
  + <p class="only-firefox">
  + <a href="https://github.com/sindresorhus/refined-github/issues/840#issuecomment-349936195" target="_blank">Not yet supported by Firefox</a>.
  </p>
  <h2>Disable features</h2>
  