Back in 2012, I wrote a userstyle to widen up Google Plus and started using one that made Google Contacts a little more compact.
Google, of course, has changed things since then.
So I updated my script and made the one for Contacts work again as well.
If you’re not already using Stylish, you probably want to give it a look. This tool can easily tweak websites to look the way you want them to look, no matter what, and works with both Firefox (and Iceweasel) and with Chrome.
The Google Plus script keeps the two column view, but widens it up:
The Google Contacts script makes better use of the screen real estate:
If you install from userstyles, it will keep you automatically updated. The scripts are also in a GitHub repository, though I was having some problems installing directly from those files.