Return about:[name] as origin for about: pages

Fix #10410

Auditors: @diracdeltas

Notes this is in the branch of code which requires muon only so it is already in unit tests but we test it with the wrong url parsing from node.

js/lib/urlutil.js

@@ -413,8 +413,9 @@ const UrlUtil = {
   },
 
   /**
-   * Gets a site origin (scheme + hostname + port) from a URL or null if not
-   * available.
+   * Gets a site origin (scheme + hostname + port) from a URL or null if not available.
+   * Warning: For unit tests, this currently runs as node without the parsed.origin
+   * branch of code, but in muon this runs through the parsed.origin branch of code.
    * @param {string} location
    * @return {string|null}
    */
@@ -429,8 +430,11 @@ const UrlUtil = {
     }
 
     let parsed = urlParse(location)
-    if (parsed.origin) {
-      // parsed.origin is specific to muon.url.parse
+    // parsed.origin is specific to muon.url.parse
+    if (parsed.origin !== undefined) {
+      if (parsed.protocol === 'about:') {
+        return [parsed.protocol, parsed.path].join('')
+      }
       return parsed.origin.replace(/\/+$/, '')
     }
     if (parsed.host && parsed.protocol) {