Instead of using a regex, use *nsINetUtil::parseContentType*:

```
    const MANIFEST_TYPE = "application/x-web-app-manifest+json";
    …
    let netUtil = Cc["@mozilla.org/network/util;1"].getService(Ci.nsINetUtil);
    let contentType = httpreq.getResponseHeader("content-type");
    if (netUtil.parseContentType(contentType, {}, {}) == MANIFEST_TYPE) {
      …
    }
    else {
      …
    }
```

Also, you might create a global lazy getter for *netUtil*, in which case I would capitalize its initial letter to more clearly identify it as a global singleton, i.e.:

```
XPCOMUtils.defineLazyGetter(this, "NetUtil", function() {
  return Cc["@mozilla.org/network/util;1"].getService(Ci.nsINetUtil);
});
```

(*XPCOMUtils* comes from the XPCOMUtils.jsm JavaScript Module, which gets imported by the debugger server into the same scope in which it loads these actors.)

Finally, note that [AppsUtils::checkManifestContentType](https://github.com/mozilla/mozilla-central/blob/72c0478d6d447598ae6e899d940257cc420e560a/dom/apps/src/AppsUtils.jsm#L341-L351) doesn't require manifests to have the application/x-web-app-manifest+json type if their origin is the same as their install origin. Perhaps we should do the same here (or simply defer to that function).