Echofon for Firefox is a fully-featured Twitter client that runs within Firefox. Unread tweets sync with your iPhone/iPad.

Echofon for Firefox is an extension that adds an Echofon button to the toolbar. When you click the button, a fully-featured Twitter client springs forth in one of three window modes. You can do all the common twitter tasks like posting tweets, viewing mentions, direct messages, lists, searches, trends, images and videos, right from Firefox.