disabled

disabled: Type: boolean; Indicates whether the element is disabled or not. If this attribute is set, the element is disabled. Disabled elements are usually drawn with grayed-out text. If the element is disabled, it does not respond to user actions, it cannot be focused, and the command event will not fire. In the case of form elements, it will not be submitted. Do not set the attribute to true, as this will suggest you can set it to false to enable the element again, which is not the case.
The disabled attribute is allowed only for form controls. Using it with an anchor tag (an <a> link) will have no effect.

The element will, however, still respond to mouse events. To enable the element, leave this attribute out entirely.; Visible controls have a disabled property which, except for menus and menuitems, is normally preferred to use of the attribute, as it may need to update additional state.

// Disabling an element
document.getElementById('buttonRemove').setAttribute("disabled", "disabled");

// Enabling back an element by removing the "disabled" attribute
document.getElementById('buttonRemove').removeAttribute("disabled");

Firefox 3.5 note

For keyset elements, support for this attribute was added in Firefox 3.5.