Some reason the browser on Downloader by AFTVnews.com app won't let you browse anymore from Mi box, but I was able to use it last night on Fire TV. I don't know a way around this issue since there is only one browser on the play store and it won't let me type anything in unless I use my phone. And some reason my phone won't connect to the Mi box anymore for some reason.
Puffin Browser let you type from keyboard and it is the best browser for Android TV (also supports flash and everything) Did you downloaded the browser plug in from 'Downloader by AFTVnews.com'. On Android TV you need to sideload the plug in from AFTVnews.com, otherwise the browser doesn't work.