This is a quick one....
When working on a Vaadin application, there are several ways to update the app's class files while sessions are still active: deploy to a server that supports session preservation, make a change to a properties file on the running server, use JRebel to push incremental changes, etc. Because the state of the UI is stored in the user's session, the changes may not be visible unless a new session is started.
You could always clear out your cookies, restart your browser, etc., but Vaadin offers a simple way to re-initialize the application so that you see the changes right away. Adding "?restartApplication" to the URL in the browser performs this function. See Debugging Vaadin Applications for more information.
If you're like me (lazy), typing "?restartApplication" more than once means there's got to be a better way. The bookmarklet below will handle this for you. Just drag it to your bookmarks bar and click it to restart the app. It takes everything in your current URL up to a question mark and then appends the magic phrase.