Make Safari open new links in existing windows as a tab, rather than a new window

When using NewsFire for checking my feeds and I click the title to read the full article, it opens it in a new window in the background in Safari. How can I make it open the articles in a new tab in the existing Safari window?

I have looked in the settings for both Safari and NewsFire, but I cannot find anything that would help me. I am guessing this is a problem with Safari, not NewsFire.

In Safari's preferences under "General" at the bottom is an item that says:

Open links from applications: in a new window or in a new tab in the current window

Make sure the radio button beside new tab in a current window is selected.

In Terminal (Applications/Utilities/Terminal), type in and run:

defaults write com.apple.Safari TargetedClicksCreateTabs -bool true

Then restart Safari.