UserChrome.css

~/Library/Application Support/Firefox/Profiles/hc82ixoy.default/chrome/userChrome.css

/* Tab bar below Navigation & Bookmarks Toolbars */

   nav-bar { /* main toolbar */

-moz-box-ordinal-group: 1 !important;
box-shadow: none !important;

}

   PersonalToolbar { /* bookmarks toolbar */

-moz-box-ordinal-group: 2 !important;

}

   titlebar { /* menu bar + tabs bar */

-moz-box-ordinal-group: 3 !important;
padding-top: 3px !important;
background-color:#fff;

}

   personal-bookmarks {margin:3px 0}
   personal-bookmarks .bookmark-item{padding-right:8px!important}

   tabbrowser-tabs {

  --user-tab-rounding: 4px;

}

.tab-background {

  border-radius: var(--user-tab-rounding) var(--user-tab-rounding) 0px 0px !important;
  margin-block: 1px 0 !important;

background-color:#eee; }

   scrollbutton-up, #scrollbutton-down { /* 6/10/2021 */

  border-top-width: 1px !important;
  border-bottom-width: 0 !important;

} /* Container color bar visibility */ .tabbrowser-tab[usercontextid] > .tab-stack > .tab-background > .tab-context-line {

  margin: 0px max(calc(var(--user-tab-rounding) - 3px), 0px) !important;

}