@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
toolbar[toolbarname="TabGroups Manager Toolbar"][class="chromeclass-toolbar"]{
display: none;
}

toolbar[toolbarname="TabGroups Manager Toolbar"][class="chromeclass-toolbar"][context="TabGroupsManagerNamespace.GroupBarContextMenu"][hidden="false"]:hover{
display: -moz-box;
}
.toolbox-top:hover > toolbar[toolbarname="TabGroups Manager Toolbar"][class="chromeclass-toolbar"][context="TabGroupsManagerNamespace.GroupBarContextMenu"][hidden="false"]{
display: -moz-box;
}