Argh! - How to force firefox to open new tabs in the background.

One of my favorite NewsBlur keyboard shortcuts is the 'o' key which opens the story in a new tab.

However, I would rather it open the story in a background tab and allow me to continue processing the story previews in the news feed.
In Chrome this works great by default, but with Firefox it took me a while to find out how to get this working. 

Thanks to a quick google search and a great lifehacker post I found the solution which worked great.
http://lifehacker.com/263940/force-links-to-open-in-the-background

The solution is to open about:config in the url bar.

Then double click the following setting: browser.tabs.loadDivertedInBackground

This should toggle the setting to true.

Enjoy!