userChrome.css

#titlebar-buttonbox {
    display: block !important;
    vertical-align: top !important;
}
.tabbrowser-arrowscrollbox scrollbox {
    overflow: visible !important;
}
.tabbrowser-arrowscrollbox scrollbox > box {
    display: block !important;
}

.tabbrowser-tabs .tabbrowser-tab {
    vertical-align: top !important;
    -moz-box-sizing: border-box !important;
    min-height: 30px !important;
    max-height: 30px !important;
}
.tabbrowser-tab:not([pinned]) {
    min-height: 30px !important;
    max-height: 30px !important;
    min-width: 60px !important;
}
.tabbrowser-tab:not([pinned])[selected] {
    min-width: 120px !important;
}
/*
.tabbrowser-tab:not([pinned]):hover {
    transition-delay: 500ms !important;
    min-width: 120px !important;
}
*/

.tabs-newtab-button {
    vertical-align: bottom !important;
    height: 30px !important;
}