Explicitly place '/' before fragment for multipage spec links

This prevents us from 301 redirecting, which could cause the fragment to
get lost

components/script/dom/webidls/HTMLSpanElement.webidl

@@ -3,5 +3,5 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-// https://html.spec.whatwg.org/multipage#htmlspanelement
+// https://html.spec.whatwg.org/multipage/#htmlspanelement
 interface HTMLSpanElement : HTMLElement {};