Haven't seen this mentioned yet, but audio and video now work in the browser while parked (it will pause if you switch to Drive). Other video sites do work but not all.
Working:
MoviesAnywhere.com
Vudu.com
PSVue.com/Watch for Live TV
Not working:
HBONow.com
Amazon Prime Video web
Watching via the browser limits fullscreen within the browser only, but there is an alternative to watch these fullscreen by opening those links from within youtube, which will take you to those sites at fullscreen. I basically added those links into an empty discussion thread on my personal youtube page.