Linkit popup won't show scrollbars in Firefox when "attributes" fieldset is expanded

The Linkit popup window won't show scrollbars when viewed in Firefox 9 or 10 (on Windows at least). When you expand the "Attributes" fieldset, some of the fields are hidden outside the window area. Other browsers automatically show scrollbars, but Firefox doesn't.

The solution seems to be to add "scrollbars" as a window property in the window.open method in editors/ckeditor/plugin.js.

Developers who don't want the disabled scrollbar to clutter up the window can then set "overflow:hidden" on body#linkit to hide the scrollbars as needed.