It's not a browser issue, rather a server issue. Your app is not found either because:
you did not properly deployed it on Tomcat
or your configuration (web.xml and/or struts.xml) is not valid.
Looking at the Tomcat web app manager would allow you to check if your app was deployed or not, ruling out one of the two possibilities.
Tomcat web app manager is a Tomcat feature which enables you to have a look on what's running on your tomcat server. You said you were using tomcat 7. I guess (I am using tomcat 6) there's a web app manager in T7. Usually you can access it thru : http://localhost:8080/manager/html.