firefox multirow

userChrome.css

/* Multi row tabs */
.tabbrowser-tab:not([pinned]) {
    flex-grow:1 !important;
    min-width:100px !important;
}

#tabbrowser-tabs .scrollbox-innerbox {
    display: flex !important;
    flex-wrap: wrap !important;
}

#tabbrowser-tabs .arrowscrollbox-scrollbox {
    overflow: visible !important;
    display: block !important;
}

.tab-stack {
    width: 100%;
    height: 100%
}