I sideloaded Thunderbird for android beta on my Chromecast HD. And for the first time I'm enjoying checking my email on the TV 🙂 The support for the remote control isn't perfect. I can open and delete emails. Selecting then icon for sending a new message doesn't work. But with the help of a game controller and a Bluetooth keyboard, I was able to send an email.
Contrast for some interface elements isn't great, but I do hope the support for Chromecast devices will get better.