userChrome.css

/* to remove elements you can use keybinds with, uncomment the line below */
/* @import "powerUser.css"; */

/* changed tabs */

.titlebar-spacer{
  display: none;
}

.titlebar-buttonbox-container{
  margin-right: 4px !important;
}

#tabbrowser-tabs{
  padding: 3px !important;
  margin-left: 2px !important;
  margin-right: 2px !important;
}

:root {
  --tab-min-height: 20px !important;
  --tab-max-height: 20px !important;
}

.tab-close-button{
  height: 15px !important;
  width: 15px !important;
  padding: 2px !important;
}

.tab-throbber-tabslist, .tab-throbber, .tab-icon-pending, .tab-icon-image, .tab-sharing-icon-overlay, .tab-icon-overlay {
    height: 14px !important;
    width: 14px !important;
}

/* navbar size */
#urlbar-input {
  height: 18px !important;
}

#urlbar{
  min-height: 25px !important;
}

.toolbarbutton-badge {
  /* min-width: 10px !important; */
}
#nav-bar > .toolbarbutton-1{
  padding: 0px !important;
}

.urlbar-page-action{
  padding-top: 2px !important;
  padding-bottom: 2px !important;
}

.notification-anchor-icon{
  padding-top: 0px !important;
  padding-bottom: 0px !important;
}

/* bookmarks size */

.bookmark-item{
  padding-top: 1px !important;
  padding-bottom: 1px !important;
}

/* Disables the bookmarks star button since it's misaligned. I use the context menu's star, so I CBA with properly fixing it. */
/* You can disable the misaligned reader view button in about:config by changing "reader.parse-on-load.enabled" to "false" btw. */
#star-button-box { display:none !important; }