Compress tabs to show dozens of them. For Firefox. How to add custom userChrome.css: https://www.userchrome.org/how-create-userchrome-css.html

screenshot.png

userChrome.css

.tabbrowser-tab {
  --tab-min-width: 55px;
  -moz-box-flex: 0 !important;
  transition: all 0.2s;
  width: -10px !important;
}

.tabbrowser-tab[visuallyselected="true"] {
  -moz-box-flex: 1 !important;
}

.tabbrowser-tabs > arrowscrollbox {
  height: 45px !important;
}