How to repair Echofon's Twitter plugin for Firefox, which authenticates with the Twitter API?

I've been using the Echofon Twitter plugin for Firefox almost as long as I've been registered with the site itself. It no longer works with Firefox, but will still install and run in the Waterfox fork. However, a recent change to the API, which also affected the Echofon mobile app, seems to have killed it off - possibly for good.

Echofon themselves no longer maintain the plugin, but the source is available on this GitHub repo echofon-firefox-unoffical

I've built a new version locally, with a new consumer key that I registered, but I'm still not able to authenticate with the API.

I think the issue is in the "buildOAuthHeader" function of the TwitterClient module where the OAuth header is built.

TwitterClient.buildOAuthHeader = function (user, method, url, param)
{
  var ts = Math.ceil(Date.now() / 1000);
  var diff = EchofonUtils.timestampDiff();
  if (diff != 0) {
    EchofonUtils.debug("local timestamp " + ts + " / server timetsamp " + (ts + diff));
    ts += diff;
  }

  var converter = Cc["@mozilla.org/intl/scriptableunicodeconverter"].createInstance(Ci.nsIScriptableUnicodeConverter);
  converter.charset = "UTF-8";
  var result = {};
  var data = converter.convertToByteArray(user + Date.now() + url + Math.random(), result);
  var ch = Cc["@mozilla.org/security/hash;1"].createInstance(Ci.nsICryptoHash);
  ch.init(ch.MD5);
  ch.update(data, data.length);
  var hash = ch.finish(false);

  var s = convertToHexString(hash);

  var oauthparam = {"oauth_consumer_key"     : OAUTH_CONSUMER_KEY,
            "oauth_timestamp"        : ts,
            "oauth_signature_method" : "HMAC-SHA1",
            "oauth_nonce"            : s + Math.random(),
            "oauth_version"          : "1.0"};

  if (user.oauth_token) {
    oauthparam["oauth_token"] = EchofonAccountManager.instance().get(user.user_id).oauth_token;
  }

  var dict = {};
  for (var key in param) dict[key] = param[key];
  for (var key in oauthparam) dict[key] = oauthparam[key];

  var paramStr = encodeURLParameter(dict);

  var base = [method, RFCEncoding(url), RFCEncoding(paramStr)].join("&");

  var signature;
  var secret = user.oauth_token_secret ? EchofonAccountManager.instance().get(user.user_id).oauth_token_secret : "";
  var signature = EchofonSign.OAuthSignature(base, secret);

  oauthparam['oauth_signature'] = signature;

  var headers = [];
  for (var key in oauthparam) {
    headers.push(key + '="' + RFCEncoding(oauthparam[key]) + '"');
  }
  headers.sort();

  return headers.join(",");
}

I'm not sure what the actual problem is, just that this is where the issue that has killed the plugin is.

When I try to authenticate with the Twitter API, I get a 401 authentication error - "Could not authenticate you"

Does anyone know the correct method to authenticate?