fenix-fox/chrome/pinned_tabs_on_right.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/pinned_tabs_on_right.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* Show pinned tabs on right side of normal tabs */
/* This is stupid hack that barely works and might lead to some very unexpected behavior */

.scrollbutton-up[orient="horizontal"]~spacer{ display: none }

.scrollbutton-up[orient="horizontal"]~scrollbox{
  -moz-box-direction: inherit; /* Fx < 112 compatibility */
  -moz-box-pack: end; /* Fx < 112 compatibility */
  justify-content: flex-end;
}

.scrollbutton-up[orient="horizontal"]~scrollbox::after{
  display: -moz-box; /* Fx < 112 compatibility */
  content: "";
  display: flex;
  flex-grow: 1;
  flex-shrink: 1;
  order: 2;
  -moz-box-flex: 1; /* Fx < 112 compatibility */
  -moz-box-ordinal-group: 2; /* Fx < 112 compatibility */
}

#tabs-newtab-button{
  -moz-box-ordinal-group: 2; /* Fx < 112 compatibility */
  order: 2;
}
.tabbrowser-tab[pinned]{
  -moz-box-ordinal-group: 3; /* Fx < 112 compatibility */
  order: 3;
}

#tabbrowser-tabs[positionpinnedtabs]{ direction: rtl }
#tabbrowser-tabs[positionpinnedtabs] > arrowscrollbox { 
  -moz-box-direction: reverse; /* Fx < 112 compatibility */
  flex-direction: row-reverse;
}
.tab-content{ direction: ltr }