help > troubleshooting > open folder
create folder "chrome"
inside folder create userChrome.css
Code: [Select] (#post_).tabbrowser-tab:not([pinned]) { flex-grow:1; min-width:150px; }
.tabbrowser-tab,.tab-background { height:40px; }
.tab-stack { width: 100%; }
#tabbrowser-tabs .scrollbox-innerbox { display: flex; flex-wrap: wrap; }
#tabbrowser-tabs .arrowscrollbox-scrollbox { overflow: visible; display: block; }
#main-window[sizemode=“maximized”] #TabsToolbar{ margin-left:var(–tab-min-height); }
#tabbrowser-tabs .scrollbutton-up,#tabbrowser-tabs .scrollbutton-down,#alltabs-button,.tabbrowser-tab:not([fadein]){ display: none; }
https://discourse.mozilla.org/t/tabs-in-two-or-more-rows-like-tabmixpro-in-quantum/21657/39 (https://discourse.mozilla.org/t/tabs-in-two-or-more-rows-like-tabmixpro-in-quantum/21657/39)