CSS menu jumping...

Please can someone help me. I have a css menu that is jumping in both firefox and Ie. Here is the code. I would appreciate any feedback, thank you and Happy New Year!!

#menubuttons {
    width: 123px ;
    text-align: center ;
}
#menubuttons ul {
    margin:2 ;
    padding: 0 ;
    list-style: none ;
}
#menubuttons li {
    font-family: Verdana, Arial, Helvetica, sans-serif;
    font-weight: bold;
    margin: 0 ;
    padding: 0 ;
    display: block ;
    width: 123px ;
    list-style: none ;
    text-decoration:  none ;
    font-size: 14px;

}
#menubuttons li a {
    color: #6100C1 ;
    background-color: #ffffff ;
    border: none ;
    width: 123px ;
    text-decoration:  none ;
    display: block ;
}
#menubuttons li a:hover {
border: solid 1px #6100C1;
background-color:#F0E1FF;
}