I haven't found much information on this extension. That icon should be an on/off switch, but if the image does not change when you click it, and any mouse over tooltip doesn't show the current status, it might be hard to confirm the status without loading a page laden with advertising.

If you want to disable the extension completely, you can do that on the Add-ons page. Either:

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then look for Bluhell Firewall on the right side and use the Disable button. If you plan to re-enable it soon, you could leave this tab open for quicker access.