All Vaadin Applications, which are not embedded via a jsp (iframe), do not show the opennms favicon.ico (see Topology Map, or Node Maps as an example)
This is probably due to a wrong URL to the favicon, which points to ./VAADIN/themes/<theme-name>/favicon.ico.
The "real" URL of the vaadin application is i.e. for the Topology Map http://localhost:8980/opennms/osgi/topology and on that page the favicon.ico is shown if it is placed in the referenced themes folder.
How the favicon location can be programmatically changed is described here: http://stackoverflow.com/questions/25660659/vaadin-how-to-change-favicon
We probably should add another service property to define the favicon?