Online/offline events could not be trigger programatically, so they have to be tested manually. To test behaviour of network monitor button, go offline and online again by doing the following:

• Firefox: Main menu → Tools → Work Offline
• IE9: File → Work offline
• IE10: Tools → Work Offline
• Opera 12 and below: Settings → Work Offline
• Chrome, Safari, IE11+, Opera 15+: No easy way. The fastest way is switching your network connection off and on via the controls your OS provides.

Button label should be "This device seems to be disconnected from the web" in offline mode, and "This device seems to be connected to the web" when you're online.

If network monitor button is not visible, this means it's not supported in this browser.