Firefox 4 has removed the Subscribe to RSS icon that was in Firefox 3.x. This icon would appear in the Location Bar when the webpage had RSS/ATOM feeds. It was useful to see if the webpage has feeds and if it did to subscribe to them.
Right-click in the Navigation Toolbar and choose Customize to get the Customize dialog. A Subscribe button is available in this dialog that provides the same functionality as the older icon did in Firefox 3.x. Pull the button to any location in the Navigation Toolbar and place it there.
Tried with: Firefox 4.0 on Windows 7