Thank you, that helped a lot. Here's my version if anyone is interested...
Additional changes:
1) Made the left hand navigation slightly grey to offset so much white.
2) Made the list of articles have less padding (more "compact", less "bloaty" :) )
3) Removed the "Home", "All Items" and "Explore" links (I never use them and just wanted it clean)
I added these to ~/.mozilla/firefox/random.User/chrome/userContent.css and restarted firefox. I wrapped the changes in a `@-moz-document domain("www.google.com")`, just in case.
Shame a CSS hack can't get the sharing features back!