When you first use Webfire you need to download the Webfire app. Once you've done this you should see the status bar on the left is showing connected. If you see failed to connect or any other message try uninstalling and reinstalling the Webfire app.
If your status usually shows connected and suddenly it's not, you may simply need to reboot your computer. This will force the app to reload. Iif you continue to have trouble getting Webfire to connect please open a support ticket.