v2

    .tabbrowser-tab .tab-close-button{
    list-style-image: url("data:image/png;base64,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") !important;
    }

    /*http://2ch.hk/s/res/1361228.html*/

    .tab-close-button {
    -moz-image-region: rect(0, 16px, 16px, 0)!important;
    }
    .tab-close-button:hover,
    .tab-close-button:hover[selected="true"] {
    -moz-image-region: rect(0, 32px, 16px, 16px)!important;
    }
    .tab-close-button:hover:active,
    .tab-close-button:hover:active[selected="true"] {
    -moz-image-region: rect(0, 48px, 16px, 32px)!important;
    }