Just for the record and for defending my necromancer badge:
For Firefox: The addon "Hide Navigation Bar" worked till version 52 came out. I don't know of any other method of hiding it.
To hide the Tabbar, the addon "Hide Tabbar" should still work. I guess it will continue to work until November 2017, when WebExtensions will be the big deal and probably break a lot of old addons like e.g. TabGroups. Just read the first few comments on the tab-groups addon page, to learn that not everyone is pleased with WebExtensions, and this to learn that probably some legacy-addons are already defunct.
I'm no addon-developer, and don't know if the situation really is that dramatic, but I'll sure miss tab-groups.
For Chrome: User Force has given the ultimate hint here, for hiding everything except the content-area. I'll use it to watch amazon prime video.