userChrome.css

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

/* Makes tabs to appear on multiple lines
         * Tab reordering will not work and can't be made to work
         * You can use multi-row_tabs_window_control_patch.css to move window controls to nav-bar
         * You might want to move tabs-new-tab-button outside tabs toolbar for smoother behavior */

/* SETTINGS (you need to create and set these prefs to true in about:config)
         * userchrome.multirowtabs.full-width-tabs.enabled  - make tabs grow horizontally to fill all available space
         * userchrome.multirowtabs.scrollbar-handle.enabled - make scrollbar in tabs box respond to mouse, makes it imposiible to drag window from empty space in tabs box */

:root {
  --multirow-n-rows: 3; /* change maximum number of rows before the rows will start to scroll */
  --multirow-tab-min-width: 100px;
  --multirow-tab-dynamic-width: 1; /* Change to 0 for fixed-width tabs using the above width. */
  --tab-min-height: 20px !important;
}

#tabbrowser-tabs {
  min-height: unset !important;
  padding-inline-start: 0px !important;
}

@-moz-document url(chrome://browser/content/browser.xhtml)
{
  #scrollbutton-up ~ spacer,
  #scrollbutton-up,
  #scrollbutton-down {
    display: var(--scrollbutton-display-model, initial);
  }

  scrollbox[part][orient="horizontal"] {
    display: flex;
    flex-wrap: wrap;
    overflow-y: auto;
    max-height: calc(
      (var(--tab-min-height) + 2 * var(--tab-block-margin, 0px)) *
        var(--multirow-n-rows)
    );
    scrollbar-color: currentColor transparent;
    scrollbar-width: thin;
    scrollbar-gutter: stable;
    scroll-snap-type: y mandatory;
  }
}

.scrollbox-clip[orient="horizontal"],
#tabbrowser-arrowscrollbox {
  overflow: -moz-hidden-unscrollable;
  display: inline;
  --scrollbutton-display-model: none;
}

.tabbrowser-tab {
  scroll-snap-align: start;
}

#tabbrowser-tabs .tabbrowser-tab[pinned] {
  position: static !important;
  margin-inline-start: 0px !important;
}

.tabbrowser-tab[fadein]:not([pinned]) {
  min-width: var(--multirow-tab-min-width) !important;
  flex-grow: var(--multirow-tab-dynamic-width) !important;
}

.tabbrowser-tab > stack {
  width: 100%;
  height: 100%;
}

/* remove bottom margin so it doesn't throw off row height computation */
#tabs-newtab-button {
  margin-bottom: 0 !important;
}

#tabbrowser-tabs[hasadjacentnewtabbutton][overflow]
  > #tabbrowser-arrowscrollbox
  > #tabbrowser-arrowscrollbox-periphery
  > #tabs-newtab-button {
  display: flex !important;
}

#alltabs-button,
:root:not([customizing]) #TabsToolbar #new-tab-button,
#tabbrowser-arrowscrollbox > spacer,
.tabbrowser-tab::after {
  display: none !important;
}

@media (-moz-bool-pref: "userchrome.multirowtabs.full-width-tabs.enabled") {
  .tabbrowser-tab[fadein]:not([pinned]) {
    max-width: 100vw !important;
  }
}
@media (-moz-bool-pref: "userchrome.multirowtabs.scrollbar-handle.enabled") {
  #tabbrowser-arrowscrollbox {
    -moz-window-dragging: no-drag;
  }
}

/* Hides native tabs bar when Sidebery is enabled. Based on https://github.com/mbnuqw/sidebery/wiki/Firefox-Styles-Snippets-(via-userChrome.css)#completely-hide-native-tabs-strip*/
/* #main-window[titlepreface*="[Sidebery]"] #titlebar { */
#main-window[titlepreface*="[Sidebery]"] #TabsToolbar {
  visibility: collapse;
  /* display: none !important; */
}

/* leaves space for the window buttons */
#main-window[titlepreface*="[Sidebery]"] #nav-bar {
  margin-right: 90px;
}

#main-window[titlepreface*="[Sidebery]"] .titlebar-buttonbox-container {
  position: fixed;
  /* display: block;  */
  top: 2px;
  right: 2px;
  background-color: var(--toolbar-bgcolor);
  height: 50px;
}

#main-window[titlepreface*="[Sidebery]"] .titlebar-buttonbox {
  background-color: rgba(43, 42, 51, 255);
}

/* title bar spacer modifications for aesethetics and making space for new tab button*/
.titlebar-spacer[type="pre-tabs"] {
  width: 2px !important;
}

.titlebar-spacer[type="post-tabs"] {
  width: 20px !important;
}

/* titlebar window button modifications for cross compatibility between native horizontal tabs view and sidebery vertical tabs view with hidden native tabs bar */
.titlebar-max {
  padding: 5px 8px 5px 10px !important;
  height: 30px;
}

.titlebar-min {
  padding: 5px 8px 5px 10px !important;
  height: 30px;
}

.titlebar-close {
  padding: 5px 8px 5px 10px !important;
  height: 30px;
}

.titlebar-restore {
  padding: 5px 8px 5px 10px !important;
  height: 30px;
}

.titlebar-buttonbox-container {
  top: 2px;
  right: 2px;
}

/* Target the new tab button's icon and increase its size */
#tabs-newtab-button .toolbarbutton-icon {
  width: 24px !important; /* Adjust the width as needed */
  height: 24px !important; /* Adjust the height as needed */
  background-size: 24px !important; /* Ensure the icon scales to the new size */
}

/* Optionally adjust the size of the new tab button itself if needed */
#tabs-newtab-button {
  min-width: 28px !important; /* Adjust the minimum width as needed */
  height: 28px !important; /* Adjust the height as needed */
  padding: 5px 0px 0px 0px !important;
}

/* Makes flexible space a smaller size */
toolbarpaletteitem[place="toolbar"][id^="wrapper-customizableui-special-spring"],
toolbarspring {
  max-width: 20px !important;
}