People and organizations are doing a lot of interesting things with Mozilla technologies. Here are two of the many Mozilla-based applications available. If you would like to suggest other applications to feature, please leave a comment.
CouchDB is an open source document-oriented database and is designed for local replication and to scale horizontally across a wide range of devices. (Uses SpiderMonkey)
ZK is the leading enterprise Ajax + Mobile framework and the easiest way to build great modern Java web applications supporting Java Mobile, Android, and various mobile browsers. (Uses XUL)