Feedly Breaks Firefox - new window opens gray

Problem

Any web page opening a new window (or if you use Shift key when clicking a link to open a new window) in Firefox resulted in a gray window and no content. The URL will be shown in the Location bar, but no content would draw, for any web page. No other problems exist with Firefox, and this problem didn't show up on any other systems I use, only this one computer.

This machine is a Windows XP laptop.

Solution

Disable or Uninstall the Feedly add-on!

Reason

Feedly version 1.0B4 is causing the damage to Firefox.
I don't know what's wrong with it, but it was the culprit.
I won't be using Feedly until it's out of Beta now.