userChrome.css

/* 
  This stylesheet is based on:
    - https://github.com/khuedoan/one-line-firefox
    - https://github.com/MrOtherGuy/firefox-csshacks
*/

/* Title bar */
.titlebar-buttonbox {
  display: none !important;
}

.titlebar-spacer {
  display: none !important;
}

/* Tab bar */
#navigator-toolbox {
  border: 0px !important;
  padding-bottom: 1px !important; /* symmetry */
}

#TabsToolbar {
  margin-left: 40vw !important; /* offset for url bar and icons */
}

#tabbrowser-tabs {
  --tab-min-height: 29px !important;
  border: none !important;
  box-shadow: none !important;
}

/* Nav bar */
#nav-bar {
  background: transparent !important;
  margin-top: -36px !important;
  margin-right: 60vw !important; /* offset for tab bar */
  padding-bottom: 1px !important; /* symmetry */
}

/* URL bar elements - uncomment selectors to _hide_ them */

/* #back-button {
  display: none !important;
} */

/* #forward-button {
  display: none !important;
} */

/* #tracking-protection-icon-container {
  display: none !important;
} */

#urlbar-container {
  min-width: 175px !important;
}

#urlbar-background {
  animation: none !important;
}

#urlbar {
  background: transparent !important;
  border: none !important;
  box-shadow: none !important;
}

#page-action-buttons {
  display: none !important;
}

#PanelUI-button {
  display: none !important;
}

/* properly display url bar pop up (history, search suggestions,...) */

:root{
  --toolbar-field-background-color: var(--toolbar-field-non-lwt-bgcolor);
  --toolbar-field-focus-background-color: var(--lwt-toolbar-field-focus,Field);
}
:root:-moz-lwtheme{
  --toolbar-field-background-color: var(--lwt-toolbar-field-background-color);
}

.urlbarView-row-inner{
   /* This sets how far the dropdown-items are from the window edge */
  padding-inline-start: 6px !important;
}

#urlbar-container,
#urlbar {
  position: static !important;
  display: -moz-box !important;
}

#urlbar {
  height: 24px !important;
  max-height: 24px !important;
  width: auto !important;
  box-shadow: inset 0 0 0 1px var(--toolbar-field-border-color, hsla(240,5%,5%,.25));
  background-color: var(--toolbar-field-background-color, hsla(0,0%,100%,.8));
  border-radius: var(--toolbarbutton-border-radius);
  --uc-urlbar-min-width: none; /* navbar_tabs_oneliner.css compatibility */
}

#urlbar[focused] {
  box-shadow: inset 0 0 0 1px var(--toolbar-field-focus-border-color, highlight);
  height: 24px !important;
  max-height: 24px !important;
}

#urlbar[focused] > *:not(.urlbarView) {
  padding: unset !important;
  padding-top: 2px !important;
  padding-left: 1px !important;
  height: 24px !important;
  max-height: 24px !important;
}

.urlbarView {
  position: absolute !important;
  margin: 0 !important;
  margin-top: 8px !important;
  left: 0 !important;
  width: 40vw !important; /* width of the urlbar pop up; set to 100vw to make it as wide as the browser window */
  border-width: 1px 0;
  top: calc(var(--urlbar-toolbar-height) + 1px); /* symmetry */
  background-color: var(--toolbar-field-focus-background-color, inherit);
  z-index: 4;
  box-shadow: 0 1px 4px rgba(0,0,0,.05);
}

#urlbar > #urlbar-input-container {
  padding: 0px !important;
  width: auto !important;
  height: 24px !important;
  max-height: 24px !important;
}

#urlbar > #urlbar-background {
  display: none !important;
}

/* This may seem pretty weird, but it gets around an issue where the height of urlbar may suddenly change when one starts typing into it */
/* If you are otherwise modifying the urlbar height then you might need to modify the height of this too */
#urlbar > #urlbar-input-container::before {
  content: "";
  display: -moz-box;
  height: 24px !important;
}