One of the biggest changes you will notice with GWT 2.0 is development mode, which

One of the biggest changes you will notice with GWT 2.0 is development mode, which
replaces what used to be called "hosted mode". Prior to 2.0, "hosted mode" provided
a special-purpose "hosted browser" to debug your GWT code. As of GWT 2.0, the web
application being debugged is viewed within a regular browser with the support of the
Google Web Toolkit Developer Plugin, which is available for most popular browsers.
*In other words, you can now develop and debug code as it runs in Safari, Firefox,*
*Internet Explorer, and Chrome.*

Selamat tinggal Opera. Kesalahan (ga sepenuhnya salah sih) dari bertaun2 lalu dengan
menutup kode dan ekstensibilitas browser.