How to Close a Browser Window or Tab with JavaScript in Firefox?

Firefox's security model dictates that a tab or window cannot be closed via JavaScript if it was not originally opened by a JavaScript command. This is a security measure to prevent scripts from closing user-initiated tabs or windows without consent. A tab or window can only be closed via JavaScript if it was initially opened by a JavaScript command.

To test this behavior:

1. Open a tab in Firefox. In the URL bar, type the following and press Enter:

javascript
    javascript:window.close();//

This action will fail to close the tab or window.

1. In a tab in Firefox, type the following in the URL bar and press Enter:

javascript
    javascript:window.open('_parent','http://www.google.com');

This will open a new tab. Navigate to that new tab and in its URL bar, type:

javascript
    javascript:window.close();

This action will successfully close the tab or window.

This demonstrates that Firefox will not permit a tab or window to be closed via JavaScript if that tab or window was not originally opened by JavaScript.