How to install and setup Sage:

In the browser menu, click on Tools then Extensions.
When the Extensions window opens, click on Get More Extensions.

Find Sage (In the News category) and install it.

After you have restarted Firefox. You will need to configure Sage.

First you need to add the Sage button to the toolbar.
Right click on the toolbar and select Customize.
Drag the Sage button to the toolbar.
Then click Done.

Clicking on the Sage button will display the Sage sidebar.
Click on Options then Settings.
Select which bookmark folder you wish to use for the feed bookmarks (links). I created a folder called "Feeds"

To add a feed to Sage, just right click on a feed’s link and select Bookmark This Link. Save it to the "Feeds" folder (or whatever you called it). That’s it.

Now all you have to do is click on the link in the Sage sidebar to read it.