>>677　userchrome.cssに以下を記述

#sidebar-box {
position: relative !important;
overflow-x: hidden !important;
margin-right: -10px !important;
left: 10px !important;
min-width: 10px !important;
max-width: 10px !important;
}

#sidebar-box:hover {
margin-right: -200px !important;
left: 200px !important;
min-width: 200px !important;
max-width: 200px !important;
}

#sidebar {
opacity: 0 !important;
}

#sidebar:hover {
opacity: 1 !important;
}

#sidebar-header {
display: none !important;
}

#sidebar-splitter {
}