compact_proton.css

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

/* Small changes to make proton roughly as compact as the old compact mode */

:root{
  --toolbarbutton-inner-padding: 6px !important;
  --tab-block-margin: 2px !important;
  --tabs-shadow-size: 0px !important;
  --arrowpanel-menuitem-padding-block: 5px !important;
  --panel-font-size: inherit !important;
  --arrowpanel-padding: 0.8em !important;
  --inline-tab-padding: 8px !important; /* 8px is default value since it looks good - lower values compactify tabs horizontally */
}
.subviewbutton.bookmark-item{ padding-block: 4px !important; }
.subview-subheader{ display: block }
menupopup > menuitem,
menupopup > menu{ padding-block: 0.3em !important; }

/* This is kinda weird, but it makes the horizontal line between tabs and nav-bar render "inside" nav-bar thus tabs are more visibily separated even if there is less space there */
#nav-bar{ 
  box-shadow: inset 0 var(--tabs-shadow-size) 0 var(--lwt-tabs-border-color) !important;
}

.tab-close-button{
  margin-inline-start: 0px !important;
  width: 20px !important;
  height: 20px !important;
  padding: 5px !important;
}

#tabbrowser-tabs{ --uc-tabs-scrollbutton-border: 2px }
#scrollbutton-up,
#scrollbutton-down{ border-block-width: var(--uc-tabs-scrollbutton-border,0px) !important; }

/* OPTIONAL - show audio label in compact mode and make the audio icon behavior match non-compact mode */
/*
.tab-secondary-label:is([soundplaying], [muted], [activemedia-blocked], [pictureinpicture]){ display: flex !important; margin-bottom: 1px }
#TabsToolbar:not(:hover) .tab-icon-image{ opacity: 1 !important; }
#TabsToolbar:not(:hover) .tab-icon-overlay:not([pinned]){ opacity: 0 !important; }
*/

firefox-revert-proton.css

:root,  #commonDialog {
  --tab-min-height: 28px !important;
  
  --toolbarbutton-inner-padding: 6px !important;
  --toolbarbutton-outer-padding: 1px !important;
  --toolbar-start-end-padding: 1px !important;
  
  --panel-font-size: 1em !important;
  --panel-separator-margin: 8px 0px !important;
  --panel-subview-body-padding: 8px 0px !important;
  
  --arrowpanel-border-radius: 0px !important;
  --arrowpanel-menuitem-padding: 4px 16px !important;
  --arrowpanel-menuitem-margin: 0px !important;
  --arrowpanel-menuitem-border-radius: 0px !important;
  
  --subdialog-font-size: 1em !important;
  
  --in-content-button-vertical-padding: 0px !important;
  --in-content-button-horizontal-padding: 8px !important;
  --in-content-primary-button-text-color: rgb(255, 255, 255) !important;
  --in-content-primary-button-background: var(--blue-60) !important;
  --in-content-primary-button-background-hover: var(--blue-70) !important;
  --in-content-primary-button-background-active: var(--blue-80) !important;
  
  --checkbox-checked-color: rgb(255, 255, 255) !important;
  --checkbox-checked-bgcolor: var(--blue-60) !important;
  --checkbox-checked-hover-bgcolor: var(--blue-70) !important;
  --checkbox-checked-active-bgcolor: var(--blue-80) !important;
  
  --focus-outline-color: var(--blue-60) !important;
  
  --blue-40: #45a1ff;
  --blue-50: #0a84ff;
  --blue-50-a30: rgba(10, 132, 255, 0.3);
  --blue-60: #0060df;
  --blue-70: #003eaa;
  --blue-80: #002275;
}

/** Titlebar */
.titlebar-buttonbox {
  margin-inline-end: -4px;
}

/** Tab */
.tabbrowser-tab {
  --tab-line-color: #0A84FF;
  --tab-label-mask-size: 2em !important;
  padding-inline: 0 !important;
}

#tabbrowser-tabs[haspinnedtabs]:not([positionpinnedtabs]) .tabbrowser-tab[first-visible-unpinned-tab] {
  margin-inline-start: 0px !important;
}

.tab-label {
  line-height: 1.7em;
}

.tab-background {
  box-shadow: none !important;
  margin-block: 0 !important;
  border-block-start: 2px solid transparent !important;
  border-radius: 0 !important;
}

.tabbrowser-tab:hover:not([selected]) .tab-background {
  border-block-start-color: color-mix(in srgb, currentColor 33%, transparent) !important;
}

[selected] .tab-background {
  background-color: var(--toolbar-bgcolor) !important;
  background-image: var(--toolbar-bgimage) !important;
  border-block-start-color: var(--tab-line-color) !important;
}

/** Tab misc. */
.tab-context-line {
  background-color: transparent !important;
  background-image: linear-gradient(to right, transparent 10%, var(--identity-tab-color) 10%, var(--identity-tab-color) 90%, transparent 90%);
  margin: -2px !important;
  transform: translateY(26px);
}

.tab-icon-image {
  opacity: 1 !important;
}

.tab-icon-overlay {
  fill-opacity: 1 !important;
  opacity: 1 !important;
  transition: none !important;
  border-radius: 10px !important;
  top: -4.5px !important;
  inset-inline-end: -9px !important;
  z-index: 1 !important;
}

.tab-icon-overlay:hover {
  background-color: white !important;
  color: black !important;
}

.tab-secondary-label {
  display: none !important;
}

.tab-close-button {
  background-image: url(chrome://global/skin/icons/close.svg);
  background-size: 14px;
  background-position: center;
  background-repeat: no-repeat;
  list-style-image: unset !important;
  width: 20px !important;
  height: 20px !important;
  padding: 2px !important;
  margin-block-start: 1px !important;
  margin-inline-end: -2px !important;
}

#tabs-newtab-button {
 padding: 0 1px !important; 
}

/** Tab border */
#tabbrowser-tabs {
  margin-inline-start: -1px !important;
}

:is(:root[sizemode='normal'], :root[gtktiledwindow='true']) .tabbrowser-tab:first-of-type {
  margin-inline-start: 1px !important;
}

.tabbrowser-tab::after,
.tabbrowser-tab::before {
  border-inline-start: 1px solid var(--toolbarbutton-active-background);
}
.tabbrowser-tab::before {
  margin-inline-start: -1px;
}

:root[tabsintitlebar]:not([extradragspace]) #toolbar-menubar[autohide=true] + #TabsToolbar .tabbrowser-tab::after,
.tabbrowser-tab:hover::after,
.tabbrowser-tab[multiselected]::after,
#tabbrowser-tabs:not([movingtab]) .tabbrowser-tab[beforehovered]::after,
#tabbrowser-tabs:not([movingtab]) .tabbrowser-tab[before-multiselected]::after {
  margin-block-start: var(--tabs-top-border-width);
  margin-block-end: 0;
}

#tabbrowser-tabs:not([movingtab]) .tabbrowser-tab[beforeselected-visible]::after,
#tabbrowser-tabs[movingtab] .tabbrowser-tab[visuallyselected]::before,
.tabbrowser-tab[visuallyselected]::after,
.tabbrowser-tab[visuallyselected]::before {
  border-color: var(--tabs-border-color);
  margin-block-start: 0;
  margin-block-end: var(--tabs-navbar-shadow-size);
}

.tabbrowser-tab::after,
.tabbrowser-tab[visuallyselected]::before,
.tabbrowser-tab:first-of-type::before,
#tabbrowser-tabs[movingtab] .tabbrowser-tab[visuallyselected]::before {
  content: '';
  display: block;
}

/** Nav bar */
#nav-bar {
  --toolbarbutton-icon-fill-attention: #45a1ff !important;
}

:where(#reload-button, #stop-button) > .toolbarbutton-icon, :where(#reload-button, #stop-button) > .toolbarbutton-animatable-box {
  translate: 0px !important;
}

/** Mega bar, Search bar */
#search-container, #urlbar-container {
  --urlbar-container-height: 32px !important;
  padding-block: 2px !important;
}

#urlbar, #searchbar {
  --urlbar-height: 26px !important;
  --urlbar-min-height: 26px !important;
  --urlbar-toolbar-height: 32px !important;
}

#urlbar-input-container {
  --urlbar-icon-padding: 4px !important;
  border: 0 !important;
}

/* TODO: figure out why the width calculation isn't working as intended. */
.urlbar-icon {
  height: 24px !important;
  width: 24px !important;
}

:is(.chromeUI, .extensionPage, .notSecureText) #identity-icon-box {
  background-color: transparent !important;
}
:is(.chromeUI, .extensionPage, .notSecureText) #identity-icon-box:hover {
  background-color: hsla(0, 0%, 70%, 0.2) !important;;
}
:is(.chromeUI, .extensionPage, .notSecureText) :is(#identity-icon-box:active, #identity-icon-box[open]) {
  background-color: hsla(0, 0%, 70%, 0.3) !important;;
}

/** Bookmarks bar */
#PersonalToolbar {
  margin-inline: -2px !important;
  padding-inline: var(--toolbar-start-end-padding) !important;
}


/** Panel */
#downloadsPanel,
#widget-overflow,
#appMenu-popup,
#customizationui-widget-panel,
#identity-popup,
#permission-popup,
#protections-popup {
  margin-block-start: -2px !important;
}

.panel-header {
  padding: 8px !important;
}

.panel-header + toolbarseparator {
  margin-block-start: 0px !important;
}

.panel-footer.panel-footer-menulike {
  margin: 0px !important;
  padding-block: 8px !important;
}

.panel-footer.panel-footer-menulike > button {
  min-height: 24px !important;
  padding: var(--arrowpanel-menuitem-padding) !important;
  margin: 0px !important;
  border-radius: var(--arrowpanel-menuitem-border-radius) !important;
}
.panel-footer.panel-footer-menulike > button:hover {
  color: inherit !important;
  outline: none !important;
}

.panel-footer.panel-footer-menulike > button label {
  margin-block: 0px !important;
}

[extension] toolbarseparator {
  margin-block-end: 0px !important;
}

.subviewbutton-back {
  transform: none !important;
  margin: 0px !important;
}

.subview-subheader {
  font-size: inherit !important;
}

.panel-subview-footer-button {
  margin-block-end: 8px !important;
}

.PanelUI-subView menuseparator {
  appearance: none !important;
}

/** Panel banner */
:is(.panel-banner-item, .addon-banner-item) {
  margin-bottom: 8px !important;
}

.addon-banner-item::after {
  margin-inline-end: 8px !important;
}

/** Main panel */
#appMenu-fxa-label2 {
  padding: var(--arrowpanel-menuitem-padding) !important;
}

#appMenu-fxa-label2 label {
  margin: 0px !important;
}

toolbarseparator.proton-zap {
  border-image: none !important;
}

#appMenu-zoom-controls2 {
  padding-inline-end: 12px !important;
}

.toolbaritem-combined-buttons:not([widget-type='button-and-view']),
.toolbaritem-menu-buttons {
  margin-inline-end: 0px !important;
}

/** Overflow panel */
#widget-overflow-mainView toolbarseparator {
  margin-block-start: 0 !important;
}

.PanelUI-subView .toolbaritem-combined-buttons > .subviewbutton {
  margin-inline-end: 0px !important;
}

/** Accounts panel */
.PanelUI-remotetabs-clientcontainer > label {
  font-size: inherit !important;
  padding-block-end: 2px !important;
  margin-inline-start: 16px !important;
}

/** Synced tabs panel */
#PanelUI-remotetabs .panel-subview-body {
  margin-block-end: 8px !important;
}

/** Downloads panel */
#downloadsPanel-blockedSubview, #downloadsPanel-mainView {
  padding: 0px !important;
}

#emptyDownloads {
  padding: var(--arrowpanel-menuitem-padding) !important;
  padding-block: 16px !important;
}

#downloadsListBox {
  margin: var(--panel-separator-margin) !important;
}

#downloadsListBox > richlistitem {
  height: 4.5em !important;
  padding: var(--arrowpanel-menuitem-padding) !important;
  padding-inline: 12px !important;
  margin: 0px !important;
  border-radius: 0px !important;
}

/** Identity security panel */
#identity-popup-securityView .identity-popup-security-content {
  border-block-end: 0px !important;
  padding-block-start: 8px !important;
  padding-block-end: 0px !important;
}

#identity-popup-securityView #identity-popup-securityView-body {
  padding-block-start: 0px !important;
  padding-block-end: 8px !important;
  margin-block: 0px !important;
  margin-inline-start: calc(2em + 16px) !important;
  margin-inline-end: 0px !important;
}

.identity-popup-security-connection {
  background-position-x: 18px !important;
  padding-block: 0px !important;
  padding-inline-start: calc(2em + 16px) !important;
  padding-inline-end: 0px !important;
}
.identity-popup-connection-secure.security-view, .identity-popup-connection-not-secure.security-view {
  margin-inline-start: 6px !important;
}

#identity-popup-security-button .identity-popup-security-connection {
  padding-inline-start: 18px !important;
}

#identity-popup-security-button {
  margin-block-end: 0px !important;
}

#identity-popup-clear-sitedata-footer,
#identity-popup-more-info-footer {
  margin-block-start: 8px !important;
}

/** Tracking protection panel */
#protections-popup-mainView-panel-header-section + toolbarseparator {
  margin-block-start: 0px !important;
}

#protections-popup-content {
  margin: 0px !important;
}

.protections-popup-tp-switch-label-box,
.protections-popup-tp-switch-box {
  min-height: unset !important;
}


#protections-popup-blocking-section-header,
#protections-popup-not-blocking-section-header,
#protections-popup-not-found-section-header {
  height: 26px !important;
  padding: 4px 16px !important;
  margin: 0px !important;
}


#protections-popup-footer {
  padding: 0px !important;
  margin-block-end: 8px !important;
}

.protections-popup-footer-button, .protections-popup-category {
  height: auto !important;
  min-height: unset !important;
}

/** Dedicated search panel */
#PopupSearchAutoComplete .search-panel-current-engine {
  padding: 4px 12px !important;
}

#PopupSearchAutoComplete .autocomplete-richlistitem {
  padding: 4px 8px !important;
}

#PopupSearchAutoComplete .search-panel-one-offs-header {
  padding: 4px 8px !important;
}

#PopupSearchAutoComplete .search-panel-one-offs-container {
  padding: 4px 8px !important;
}

#PopupSearchAutoComplete .search-setting-button {
  min-height: unset !important;
  padding: var(--arrowpanel-menuitem-padding) !important;
  border-radius: var(--arrowpanel-menuitem-border-radius) !important;
}

#PopupSearchAutoComplete .search-setting-button .button-box {
  -moz-box-pack: start !important;
}


/** Notification bar (DRM etc) */
notification-message:not([style*='margin']) {
  margin: 0px !important;
}

.container.infobar {
  border-radius: 0px !important;
}

.container.infobar::before {
  content: unset !important;
}

.container.infobar .icon {
  color: currentColor !important;
  margin-block: auto !important;
  margin-inline-start: calc(8px + 3px) !important;
}

.container.infobar .notification-content {
  display: flex !important;
  justify-content: space-between !important;
  width: -moz-available !important;
  margin-inline-start: calc(8px + 3px) !important;
}

.container.infobar .notification-message {
  margin-inline-end: 8px !important;
}

.container.infobar .notification-button {
  margin: 0px !important;
}

.container.infobar .notification-button.primary {
  --in-content-primary-button-text-color: rgb(255, 255, 255) !important;
  --in-content-primary-button-background: var(--blue-60) !important;
  --in-content-primary-button-background-hover: var(--blue-70) !important;
  --in-content-primary-button-background-active: var(--blue-80) !important;
}

.container.infobar .close {
  margin: auto 8px !important;
}

/** UI controls */
panel {
  --buttons-primary-button-color: rgb(255, 255, 255) !important;
  --buttons-primary-button-bgcolor: var(--blue-60) !important;
  --buttons-primary-button-hover-bgcolor: var(--blue-70) !important;
  --buttons-primary-button-active-bgcolor: var(--blue-80) !important;
}

.panel-footer > button {
  font-weight: normal !important;
  min-width: 6.3em !important;
  min-height: 32px;
  padding: 0 8px !important;
}

.checkbox-check[checked] {
  background-size: 14px !important;
}

menulist {
  min-height: 32px !important;
  padding: 0 8px !important;
}

/** Dialogs */
.dialogBox {
  border-radius: 2px !important;
}

@-moz-document url('chrome://global/content/commonDialog.xhtml'),
    url('chrome://mozapps/content/handling/permissionDialog.xhtml'),
    url('chrome://mozapps/content/handling/appChooser.xhtml'),
    url-prefix("chrome://global/content/print.html")
{
  #commonDialog {
    --subdialog-font-size: 1em !important;
    --in-content-button-vertical-padding: 0px !important;
    --in-content-button-horizontal-padding: 8px !important;
    --in-content-primary-button-text-color: rgb(255, 255, 255) !important;
    --in-content-primary-button-background: var(--blue-60) !important;
    --in-content-primary-button-background-hover: var(--blue-70) !important;
    --in-content-primary-button-background-active: var(--blue-80) !important;
  }

  #commonDialog[subdialog] {
    padding: 16px 10px !important;
  }
  
  button {
    font-weight: normal !important;
  }
}

tabs_on_bottom.css

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

/* IMPORTANT
Get window_control_placeholder_support.css
Window controls will be all wrong without it.
Additionally on Linux, you may need to get:
linux_gtk_window_control_patch.css

Use tabs_on_bottom_menubar_on_top_patch.css if you
have menubar permanently enabled and want it on top 
*/

#toolbar-menubar[autohide="true"] > .titlebar-buttonbox-container,
#TabsToolbar > .titlebar-buttonbox-container{
  position: fixed;
  display: block;
  top: 0px;
  right:0;
  height: 40px;
}
@media (-moz-bool-pref: "userchrome.force-window-controls-on-left.enabled"),
       (-moz-gtk-csd-reversed-placement),
       (-moz-platform: macos){
  .titlebar-buttonbox-container{ left:0; right: unset !important; }
}

:root[uidensity="compact"] #TabsToolbar > .titlebar-buttonbox-container{ height: 32px }

#toolbar-menubar[inactive] > .titlebar-buttonbox-container{ opacity: 0 }

.titlebar-buttonbox-container > .titlebar-buttonbox{ height: 100%; }

#titlebar{
  order: 2;
  -moz-appearance: none !important;
  --tabs-navbar-shadow-size: 0px;
  --uc-menubar-vertical-overlap: 19px; /* for hide_tabs_with_one_tab_w_window_controls.css compatibility */
}
/* Re-order window and tab notification boxes */
#navigator-toolbox > div{ display: contents }
.global-notificationbox,
#tab-notification-deck{
  order: 2;
}

#TabsToolbar .titlebar-spacer{ display: none; }
/* Also hide the toolbox bottom border which isn't at bottom with this setup */
#navigator-toolbox::after{ display: none !important; }

@media (-moz-gtk-csd-close-button){
  .titlebar-button{
    flex-direction: column;
  }
}

/* At Activated Menubar */
:root:not([chromehidden~="menubar"], [sizemode="fullscreen"]) #toolbar-menubar:not([autohide="true"]) + #TabsToolbar > .titlebar-buttonbox-container {
  display: block !important;
}
#toolbar-menubar:not([autohide="true"]) > .titlebar-buttonbox-container {
  visibility: hidden;
}

/* These exist only for compatibility with autohide-tabstoolbar.css */
toolbox#navigator-toolbox > toolbar#nav-bar.browser-toolbar{ animation: none; }
#navigator-toolbox:hover #TabsToolbar{ animation: slidein ease-out 48ms 1 }
#TabsToolbar > .titlebar-buttonbox-container{ visibility: visible }
:root:not([lwtheme]) #navigator-toolbox{ background-color: -moz-dialog }

/* Uncomment the following if you want bookmarks toolbar to be below tabs */
/*
#PersonalToolbar{
  order: 2;
}
*/

tabs_on_bottom_menubar_on_top_patch.css

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

/* Menubar on top patch - use with tabs_on_bottom.css */
/* Only really useful if menubar is ALWAYS visible */

:root:not([sizemode="fullscreen"]){ --uc-window-control-width: 0px !important }

:root{
   /* height if native titlebar is enabled, assumes empty menubar */
  --uc-menubar-height: 20px;
}
:root[tabsintitlebar]{
  /* height when native titlebar is disabled, more roomy so can fit buttons etc. */
  --uc-menubar-height: 29px;
}
:root:is([sizemode="fullscreen"],[chromehidden~="menubar"]){
  --uc-menubar-height: 0px;
}
/* Since menubar is statically at top, remove fake drag-space that might be set by window_control_placeholder_support.css */
:root:not([sizemode="fullscreen"]) #nav-bar{ border-inline-width: 0 }

#navigator-toolbox{
  -moz-window-dragging: drag;
  padding-top: var(--uc-menubar-height) !important;
}

/* Remove window dragging from notification boxes */
#tab-notification-deck,
.global-notificationbox{
  -moz-window-dragging: no-drag;
}

:root:not([chromehidden~="menubar"]) #toolbar-menubar{
  position: fixed;
  display: flex;
  top: 0px;
  height: var(--uc-menubar-height);
  width: 100%;
  overflow: hidden;
}

#toolbar-menubar > .titlebar-buttonbox-container{ height: 100%; order: 100; }

#toolbar-menubar > [flex]{ flex-grow: 100; }
#toolbar-menubar > spacer[flex]{
  order: 99;
  flex-grow: 1;
  min-width: var(--uc-window-drag-space-post,20px);
}

#toolbar-menubar .toolbarbutton-1 { --toolbarbutton-inner-padding: 3px }

:root:not([sizemode="fullscreen"]) #toolbar-menubar.browser-toolbar > .titlebar-buttonbox-container{
  visibility: visible;
}
:root:not([chromehidden~="menubar"], [sizemode="fullscreen"]) #TabsToolbar#TabsToolbar#TabsToolbar > .titlebar-buttonbox-container {
  display: none !important;
}

tabs_on_bottom_v2.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/tabs_on_bottom_v2.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* This reorders toolbar to place tabs below other toolbars. Requires Firefox 133+ */

@media (-moz-bool-pref: "userchrome.force-window-controls-on-left.enabled"){
  #nav-bar > .titlebar-buttonbox-container{
    order: -1 !important;
    > .titlebar-buttonbox{
      flex-direction: row-reverse;
    }
  }
}
@media not (-moz-bool-pref: "sidebar.verticalTabs"){
  .global-notificationbox,
  #tab-notification-deck,
  #TabsToolbar{
    order: 1;
  }
  #TabsToolbar > :is(.titlebar-spacer,.titlebar-buttonbox-container){
    display: none;
  }
  :root[sizemode="fullscreen"] #nav-bar > .titlebar-buttonbox-container{
    display: flex !important;
  }
  :root[tabsintitlebar] #toolbar-menubar:not([autohide="false"]) ~ #nav-bar{
    > .titlebar-buttonbox-container{
      display: flex !important;
    }
    :root[sizemode="normal"] & {
      > .titlebar-spacer{
        display: flex !important;
      }
    }
    :root[sizemode="maximized"] & {
      > .titlebar-spacer[type="post-tabs"]{
        display: flex !important;
      }
      @media (-moz-bool-pref: "userchrome.force-window-controls-on-left.enabled"),
        (-moz-gtk-csd-reversed-placement),
        (-moz-platform: macos){
        > .titlebar-spacer[type="post-tabs"]{
          display: none !important;
        }
        > .titlebar-spacer[type="pre-tabs"]{
          display: flex !important;
        }
      }
    }
  }
}

userChrome.css

@import url(tabs_on_bottom.css);
@import url(tabs_on_bottom_v2.css);
@import url(tabs_on_bottom_menubar_on_top_patch.css);
@import url(firefox-revert-proton.css);
@import url(compact_proton.css);