how to remove only one style property with jquery

The documentation for css() says that setting the style property to the empty string will remove that property if it does not reside in a stylesheet:

Setting the value of a style property to an empty string — e.g. $('#mydiv').css('color', '') — removes that property from an element if it has already been directly applied, whether in the HTML style attribute, through jQuery's .css() method, or through direct DOM manipulation of the style property. It does not, however, remove a style that has been applied with a CSS rule in a stylesheet or <style> element.

Since your styles are inline, you can write:

$(selector).css("-moz-user-select", "");