In Firefox, there is a setting that can allow or disallow scripts from opening your browser window.

1. Type about:config in the address bar and press Enter.

2. Find the setting dom.allow_scripts_to_close_windows.

3. Double-click on the setting to set it to true to enable scripts to close the browser window via close(). Set it to false to prevent scripts from closing windows via close().

Note: This setting is available in Firefox 3 and Firefox 2.