Please check Thomas sir's reply in this thread: http://scn.sap.com/thread/1406302
Also this help doc:
Hope this helps u.,
The reply indicates that, if you change the default browser of OS, it won't work.
Web Dynpro HTML Control wraps around IE and it is complicated to change the default browser of WDA.
Where as from SICF you can test with default broswer. But end user will not go each time to SICF to test..!!
1. Make Google Chrome your default browser.
2. Test your Webdynpro Applications from SICF .