Firefox userChrome.css

/* TABS: on bottom */
#navigator-toolbox toolbar:not(#nav-bar):not(#toolbar-menubar)
{
  -moz-box-ordinal-group:10
  margin-top: 0px
  margin-bottom: 0px
}
#TabsToolbar
{
 -moz-box-ordinal-group:1000 !important
}

#TabsToolbar {
 position: absolute !important;
 bottom: 0 !important;
 width: 100vw !important;
 background-color: var(--toolbar-bgcolor) !important;
}

#tabbrowser-tabs {
  width: 100vw !important;
}

/* drag space */
.titlebar-spacer[type="pre-tabs"],
.titlebar-spacer[type="post-tabs"] {
  display:none !important;
}

#main-window:not([chromehidden*="toolbar"]) #navigator-toolbox
{
  padding-bottom: var(--tab-min-height) !important;
}

/* TABS: height */
:root {
 --tab-toolbar-navbar-overlap: 0px !important;
 --tab-min-height: 25px !important; /* adjust to suit your needs */
}
:root #tabbrowser-tabs {
 --tab-min-height: 25px !important; /* needs to be the same as above under :root */
 --tab-min-width: 80px !important;
}

#TabsToolbar {
 height: var(--tab-min-height) !important;
 margin-bottom: 1px !important;
 box-shadow: ThreeDShadow 0 -1px inset, -moz-dialog 0 1px !important;
 background-color: var(--toolbar-bgcolor) !important;
}

/* Fixes window moving when moving a tab */
#navigator-toolbox[movingtab] > #titlebar > #TabsToolbar {
  padding-bottom: unset !important;
}
#navigator-toolbox[movingtab] #tabbrowser-tabs {
  padding-bottom: unset !important;
  margin-bottom: unset !important;
}
#navigator-toolbox[movingtab] > #nav-bar {
  margin-top: unset !important;
}

/* Fixes window buttons being on window area */
.titlebar-buttonbox-container{
  position: fixed;
  top:0;
  left:0;
  height: 0px;
}

/* Hides favicons in the bookmarks bar. */
#personal-bookmarks .toolbarbutton-icon
{
  display: none !important;
}