From SyncError: "We are happy to announce the first release of the new QUAKE LIVE standalone client. Existing users can easily upgrade by logging in, and downloading the installer when asked. Running QUAKE LIVE from the Start Menu or Desktop will now update your game through the launcher, before loading up QUAKE LIVE and logging you into the website from the built in browser."

A FAQ about the transition from browser based to client support provided by id Software was released and is listed below.

Links: Official News post