How do you get a dark theme in new thunderbird (45.0)? My eyes hurt during the dark with white content. I wish all of the content to be dark.

Go to '''Tools|Add-ons''', use the search box to look for ''themes''. Or look here: https://addons.mozilla.org/en-GB/thunderbird/complete-themes/ I think you'll need a so-called "Complete Theme". The more common "lightweight" themes usually just add some colouring to the title bar.