The Pause button is only available when a refreshing process is going on. It appears above the Feeds toolbar, replacing the version number.
Pausing a refresh cycle is possible by clicking on the pause button or the 'Checking...' text. The refresh is not paused until the current feed has been processed, until then 'Pausing' appears as the text.
about:config
The button can be suppressed by creating
newfox.advanced.showPauseButton
and setting it equal to false. pausing is still possible by clicking the text. Styling in newsfox.css is possible, here is the default:
#pause-icon
{ list-style-image: url("chrome://newsfox/skin/images/pause.png"); }
#play-icon
{ list-style-image: url("chrome://newsfox/skin/images/play.png"); }