userChrome.css

.tab-label-container[textoverflow]:not([pinned]) {mask-image: none !important;}

#tabbrowser-tabs[closebuttons="activetab"] .tab-close-button:not([selected]):not([pinned]) {
    display: flex !important;
    visibility: collapse !important;
}
#tabbrowser-tabs[closebuttons="activetab"] .tabbrowser-tab:hover .tab-close-button:not([selected]):not([pinned]) {
    transition-delay: 350ms !important;
    visibility: initial !important;
}
.tabbrowser-tab:not([pinned]):not(:hover) .tab-close-button {
  visibility: collapse !important;
}
.tabbrowser-tab:not([pinned]):hover .tab-close-button {
  visibility: visible !important;
  display: block !important;
}

/* tab close icon size and position */
.tabbrowser-tab:not([pinned]) .close-icon > .toolbarbutton-icon {
  width: 16px !important;
  height: 16px !important;
  -moz-margin-end:-4px !important;
}

/* Reduce tab min-width */
.tabbrowser-tab[fadein]:not([pinned]) {
  min-width: 65px !important;
  max-width: 250px !important;
}

#tabbrowser-arrowscrollbox > .arrowscrollbox-scrollbox {
-moz-padding-end: 22px !important;
-moz-padding-start: 0px !important;
}

.tab-line{ display: none !important; }

#PersonalToolbar { padding-bottom: 5px !important; }

#context-back, #context-forward, #context-reload, #context-stop, #context-bookmarkpage, #spell-no-suggestions, #spell-add-to-dictionary, #spell-undo-add-to-dictionary, #context-openlinkincurrent, #context-openlinkincontainertab, #context-openlinkinusercontext-menu, #greasemonkey-view-userscript, #context-openlink, #context-openlinkprivate, #RIL_context_saveLink, #context-bookmarklink, #context-sharelink, #context-savelink, #context-media-playbackrate, #context-media-showcontrols, #context-media-hidecontrols, #context-video-fullscreen, #context-leave-dom-fullscreen, #context-viewimage, #context-viewvideo, #context-copyimage-contents, #context-shareimage, #context-sendimage, #context-setDesktopBackground, #context-sharevideo, #context-sendvideo, #context-castvideo, #context-sendaudio, #context-sharepage, #context-savepage, #context-sendpagetodevice, #context-cut, #context-delete, #context-selectall, #context-keywordfield, #context-searchselect, #context-sendlinktodevice, #context-shareselect, #frame, #context-viewpartialsource-selection, #context-viewpartialsource-mathml, #context-viewsource, #context-viewinfo, #spell-check-enabled, #spell-add-dictionaries-main, #spell-dictionaries, #context-inspect, #context-media-eme-learnmore, #RIL_context_clickMode, #RIL_context_savePage, #sync-tabs-menuitem, #sanitizeItem, #context-sep-navigation, #context-sep-sendpagetodevice, #context-sep-viewbgimage, #context-viewbgimage, #context-sep-viewsource, #inspect-separator, #context-navigation, #mozilla_cc3_internetdownloadmanager_com-menuitem-3, #mozilla_cc3_internetdownloadmanager_com-menuitem-4, #contentAreaContextMenu > menuseparator:nth-child(90), #historyUndoWindowMenu, #context_toggleMuteTab, #context_pinTab, #context-inspect-a11y , #context_openANewTab, #context_openANewTab+menuseparator {display: none !important;}

/* increase firefox font size */
* { font-size: 12pt !important; }

/* Completely hide the "title changed" notification dot on pinned tabs */
  .tabbrowser-tab > .tab-stack > .tab-content[pinned][titlechanged] {
    background-image: none !important;
  }

/*AGENT_SHEET*/
#main-window #navigator-toolbox #TabsToolbar .tabbrowser-tab[pinned][titlechanged]:not([selected="true"]):not(:hover)
{
    /* change background to a more visible highlighting */
  background-image: linear-gradient(to top, rgb(149, 188, 255), rgb(226, 234, 242)) !important;
  background-image: linear-gradient(to bottom, rgb(149, 188, 255), rgb(226, 234, 242)) !important;
}

/* move titlebar and its content (menubar, tabs toolbar) below navigation/bookmarks toolbar */
#titlebar {
  order: 100 !important;
}

/* space above tabs toolbar */
#main-window[tabsintitlebar][sizemode="0"] * #titlebar {
  margin-top: -8px !important;
}

/* space for menubar above navigation toolbar (Firefox titlebar) */
#main-window[tabsintitlebar]:not([sizemode="fullscreen"]) #nav-bar {
  margin-top: 26px !important;
}
#main-window[tabsintitlebar][sizemode="0"]:not([sizemode="fullscreen"]) #nav-bar {
  margin-top: 26px !important;
}

/* add 'drag' feature to space above navigation toolbar */
#main-window[tabsintitlebar] #navigator-toolbox,
#main-window[tabsintitlebar] #nav-bar {
  -moz-window-dragging: drag !important;
}

/* move menubar to the top and extend its with to full window width */
#toolbar-menubar {
  position: fixed !important;
  width: 100vw !important;
  display: flex !important;
  -moz-window-dragging: drag !important;
}

/* menubar postion after moving to the top */
#toolbar-menubar {
  top: 0px !important;
}

@media (-moz-platform:windows-win10) {
	/* set to '0', if no menubar is used */
	#main-window:not([tabsintitlebar]):not([sizemode="fullscreen"]) #nav-bar {
	  margin-top: 18px !important;
	}
	/* set to '0', if no menubar is used */
	#main-window[tabsintitlebar][sizemode="0"]:not([sizemode="fullscreen"]) #nav-bar {
	  margin-top: 34px !important;
	}
	#main-window[tabsintitlebar][sizemode="0"] #toolbar-menubar {
	  top: 8px !important;
	}
	#main-window[tabsintitlebar]:not([inDOMFullscreen="true"]) .titlebar-buttonbox-container {
	  top: 0px !important;
	}
	#main-window[tabsintitlebar][sizemode="0"]:not([inDOMFullscreen="true"]) .titlebar-buttonbox-container {
	  top: 8px !important;
	}
}

/* hide line above navigation toolbar appearing in some cases */
#main-window:not([tabsintitlebar]) #nav-bar,
#main-window:not([tabsintitlebar]) #navigator-toolbox {
  border-top: 0 !important;
  box-shadow: unset !important;
}

/* force buttons on menubar being very small to not break the toolbar */
#toolbar-menubar toolbaritem > toolbarbutton .toolbarbutton-icon,
#toolbar-menubar > toolbarpaletteitem toolbarbutton .toolbarbutton-icon,
#toolbar-menubar > toolbarbutton .toolbarbutton-icon {
  padding: 0px 0px !important;
  height: 16px !important;
  width: 16px !important;
}
#toolbar-menubar toolbaritem > toolbarbutton,
#toolbar-menubar > toolbarpaletteitem toolbarbutton,
#toolbar-menubar > toolbarbutton {
  position: relative !important;
  padding: 0px 0px !important;
  margin: 0px 0px !important;
}
#toolbar-menubar toolbaritem > toolbarbutton .toolbarbutton-icon,
#TabsToolbar-customization-target > toolbarpaletteitem toolbarbutton .toolbarbutton-icon,
#TabsToolbar-customization-target > toolbarbutton .toolbarbutton-icon {
  padding: unset !important;
  height: unset !important;
  width: unset !important;
}

/* make sure button icon colors set correctly */
#main-window:not(:-moz-lwtheme) #TabsToolbar-customization-target toolbarbutton .toolbarbutton-icon,
#main-window:not([style*='--lwt-header-image']):-moz-lwtheme:-moz-lwtheme-darktext #TabsToolbar-customization-target toolbarbutton .toolbarbutton-icon {
  fill: var(--classic_squared_tabs_new_tab_icon_color) !important;
  color: var(--classic_squared_tabs_new_tab_icon_color) !important;
}

/* tweaks for fullscreen mode */
#main-window[tabsintitlebar][sizemode="fullscreen"] * #TabsToolbar {
 -moz-padding-start: 0px !important;
}
/* tweaks for fullscreen mode */
#main-window[tabsintitlebar][sizemode="fullscreen"]:not([inDOMFullscreen="true"]) .titlebar-buttonbox-container,
#main-window[tabsintitlebar][sizemode="fullscreen"] #toolbar-menubar[autohide="true"] ~ #TabsToolbar .titlebar-buttonbox-container,
#main-window[tabsintitlebar][sizemode="fullscreen"] #navigator-toolbox #PanelUI-button,
#main-window #TabsToolbar #window-controls {
  display: none !important;
}

/* hide non-required items */
#TabsToolbar .private-browsing-indicator,
#TabsToolbar #window-controls,
#TabsToolbar *[type="caption-buttons"],
#TabsToolbar *[type="pre-tabs"],
#TabsToolbar *[type="post-tabs"] {
  display: none !important;
}

/* Windows 10 extra tweaks */
@media (-moz-platform: windows-win10) {
  #main-window:not([tabsintitlebar]) menubar > menu:not(:-moz-lwtheme):hover:not([disabled="true"]),
  #main-window:not([tabsintitlebar]) menubar > menu:not(:-moz-lwtheme)[_moz-menuactive="true"]:not([disabled="true"]) {
	background-color: Highlight !important;
	color: HighlightText !important;
  }
}

/* disable Mozillas tab jumping nonsense when moving tabs */
#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;
}

findbar:not(:focus-within) {
  height: 0px !important;
  overflow: hidden !important;
}

findbar {
background-color: inherit !important; /*color , set "inherit" for default */
border-radius: 0px !important; /*square corners */
color: inherit !important; /*text color */
}

/* Remove new Megabar grow & shrink effect */
#urlbar:not(.megabar):-moz-lwtheme, #urlbar.megabar:-moz-lwtheme > #urlbar-background,
#navigator-toolbox #searchbar:not(:focus-within):-moz-lwtheme {
  	border: none !important;
}

#PlacesToolbarItems > .bookmark-item { padding-block: 1px !important; }

/* This style makes tabs and related items non-rounded and connects tabs to toolbars like in previous Firefox versions. */

:root[id]{
  --proton-tab-block-margin: 0px !important;
  --tab-block-margin: 0px !important;
  --tabs-shadow-size: 1px !important;

  /* Remove next line if you want selected tab to have color other than toolbar background - then it follows your theme color  */
  --lwt-selected-tab-background-color: var(--toolbar-bgcolor) !important;
}

/* These next two rules set a color for border around tabs and between tabs & navigation toolbars. Set to transparent to remove the border.*/
#nav-bar{

/* This overrides value in compact_proton.css */
  box-shadow: 0 -1px 0 0 color-mix(in srgb, currentcolor 30%, transparent) !important;
}
.tab-background[selected]{
  border-inline: 1px solid color-mix(in srgb, currentcolor 30%, transparent) !important;
}

#TabsToolbar{
  --toolbarbutton-inner-padding: 7px !important;
}
#navigator-toolbox:not([movingtab]) > #titlebar > #TabsToolbar{
  --toolbar-bgcolor: transparent;
}

#TabsToolbar .toolbarbutton-1 > .toolbarbutton-badge-stack,
#TabsToolbar .toolbarbutton-1 > .toolbarbutton-icon{ border-radius: 2px !important;  }

#scrollbutton-up,
#scrollbutton-down{ border-radius: 0 !important; border-width: 0 !important; padding-inline: 3px !important; }

/* tab shaping */
.tabbrowser-tab{ padding-inline: 0 !important; }

:root[uidensity="compact"] #tabbrowser-tabs[positionpinnedtabs] .tabbrowser-tab[pinned]{ min-height: calc(var(--tab-min-height) + 2px) !important; }

.tab-content[pinned]{ padding-inline: 11px !important; }

.tab-background{
  border-radius: 0 !important;
  box-shadow: none !important;
}

/* Line to mark selected tab */
.tab-background[selected]::before,
.tabbrowser-tab:hover > stack > .tab-background::before{
  display: flex;
  height: 2px;
  content: "";
}
.tab-stack:hover > .tab-background::before{
  background-color: inherit;
}
.tab-stack > .tab-background[selected]::before{
  background-color: highlight;
  background-image: linear-gradient(var(--tab-line-color),var(--tab-line-color));
}

/* Photon-like tab on hover animation for the top line */
@keyframes tab-onhover-line-anim{ from{ margin-inline: 20px } to { margin-inline: 0 } }

.tab-stack:hover > .tab-background::before{ animation: tab-onhover-line-anim 160ms }

/* Disable animation for selected and pinned tabs */
.tabbrowser-tab:is([pinned],[selected]) > .tab-stack > .tab-background::before{ animation: none }

/* Bring back tab separator lines that were removed in Proton */

.tabbrowser-tab:not(:hover, [beforehovered], [selected], [last-visible-tab], [beforeselected-visible])::after {
  content: "";
  display: block;
  border-left: 1px solid currentColor;
  margin-block: 1px;
  margin-left: -1px;
  opacity: 0.3;
}

/* Shows tab audio icons next to the tab icon, and by default removes the tab secondary line */
.tabbrowser-tab:not([pinned]) .tab-icon-stack:is([muted],[soundplaying],[activemedia-blocked]){
  grid-template-areas: "a s";
}
.tabbrowser-tab:not([pinned]) .tab-icon-overlay:is([muted],[soundplaying],[activemedia-blocked]){ grid-area: s; }
.tab-icon-overlay,.tab-icon-image{ opacity: 1 !important; }

/* secondary audio label ain't much use with this style, but feel free to remove the next line if you want to show it. */
.tab-secondary-label{ display: none }

/* show the secondary label when video is in PiP */
.tab-secondary-label[pictureinpicture]{ display: flex }

/*Tighten up drop-down/context/popup menu spacing */

menupopup > menuitem, menupopup > menu {
padding-block: 2px !important;
}
:root {
--arrowpanel-menuitem-padding: 2px 8px !important;
}

.tab-label-container{ height: unset !important; }

.tab-background {
    outline: none !important;
}