Extensions are software programs that extend the capabilities of the browser in a specific way.
The Mozilla Firefox Extensions tool allows you to disable or uninstall any extension.
When an extension is active, a blue checkmark is present in the circle to its left. Also, on the right section you will see a green dot and the word "active". To make it inactive, simply click the circle so the checkmark disappears. On the right you will see a red dot and the word "inactive". To delete an extension, hover over it and then click the red trash can button.