:set toolbars=nonavigation,notabs
(it will remove tabs and the navigation menu)[0] https://addons.mozilla.org/en-US/firefox/addon/littlefox-for...
Don't put the tabs on the top of the screen. You are probably concerned about vertical real estate because you have a 16:9 display. Horizontal bars just don't make sense any more.
Install the Tree Style Tab extension. Shove all your tabs into a sidebar. Now your browser has an eye-friendly aspect ratio. Plus you can have more than twenty tabs open at once without reducing the page title to a mere favicon.
Personally I wouldn't care if it looked ugly as long as it renders stuff right.
personally I use it along-side
https://addons.mozilla.org/en-US/firefox/addon/ft-deepdark/
http://i.imgur.com/AvBjeSz.png is the result on windows 8 with a bit of settings changes
And the UI to be used? I haven't clicked a UI element in any browser manually for years (at least that what it feels like).