#titlebar-buttonbox {
display: block !important;
vertical-align: top !important;
}
.tabbrowser-arrowscrollbox scrollbox {
overflow: visible !important;
}
.tabbrowser-arrowscrollbox scrollbox > box {
display: block !important;
}
/* タブの高さ・横幅設定 */
.tabbrowser-tab:not([pinned]) {
min-height: 30px !important;
max-height: 30px !important;
min-width: 170px !important;
}
.tabbrowser-tabs .tabbrowser-tab {
vertical-align: top !important;
-moz-box-sizing: border-box !important;
min-height: 30px !important;
max-height: 30px !important;
}
/* 新しいタブボタン設定 */
.tabs-newtab-button {
vertical-align: bottom !important;
height: 30px !important;
}
https://addons.mozilla.org/ja/firefox/addon/new-tab-from-location-bar/