Firefox-UI-Fix/src/decoration/_animate.scss

/*- Background Color -------------------------------------------------------*/
@import "./animate_common";

//-- Mixin ---------------------------------------------------------------------
@mixin _animate_bgColor($duration, $presudo: "") {
  button#{$presudo},
  toolbarbutton#{$presudo},
  stack#{$presudo},
  vbox#{$presudo},
  .toolbarbutton-icon#{$presudo},
  #tabs-newtab-button#{$presudo} > .toolbarbutton-icon {
    transition: background-color $duration var(--animation-easing-function) !important;
  }
}

//------------------------------------------------------------------------------

@include _animate_bgColor(1s);
@include _animate_bgColor(0.25s, ":hover");
@include OS($linux) {
  @include not_lwtheme {
    .tabbrowser-tab:is([visuallyselected], [multiselected], [selected]) .tab-background {
      transition: background-image 0.25s var(--animation-easing-function) !important;
    }
  }
}

.subviewbutton {
  /* treechildren::-moz-tree-row: Can't apply
     menu, menuitem is not apply.
   */
  transition: background-color 0.5s var(--animation-easing-function) !important;
  &:hover {
    transition: background-color 0.1s var(--animation-easing-function) !important;
  }
}

/*- Pinned Tab -------------------------------------------------------------*/
#tabbrowser-tabs:not([movingtab]) {
  .tabbrowser-tab {
    &:not([collapsed]) {
      /* -moz-box-flex may be caused #tabbrowser-tabs[closebuttons] */
      transition: -moz-box-flex 0.2s var(--animation-easing-function),
        flex 0.2s var(--animation-easing-function),
        margin-inline-start 0.2s var(--animation-easing-function), min-width 0.1s ease-out, max-width 0.1s ease-out !important;
    }
    &[pinned] {
      transition: margin-inline-start 0.2s var(--animation-easing-function), min-width 0.1s ease-out, max-width 0.1s ease-out !important;
    }
  }

  .tab-content {
    &::before,
    &::after {
      transition: width 0.2s var(--animation-easing-function), transform 0.2s var(--animation-easing-function) !important;
    }
    .tab-label-container {
      transition: width 0.3s var(--animation-easing-function) !important;
    }
    .tab-icon-image {
      transition: all 0.3s var(--animation-easing-function) !important;
    }
  }
}

/*- URL / Search Bar -------------------------------------------------------*/
#urlbar-background,
#searchbar {
  transition: border-color 1s var(--animation-easing-function), background-color 1.5s var(--animation-easing-function) !important;
  &:hover {
    transition: border-color 0.5s var(--animation-easing-function), background-color 1s var(--animation-easing-function) !important;
  }
}

/* Buttons in URL bar */
#tracking-protection-icon-container,
#identity-icon-box,
#identity-permission-box,
#notification-popup-box,
#page-action-buttons > .urlbar-page-action {
  transition: background-color 2.5s var(--animation-easing-function) !important;
  &:hover {
    transition: background-color 1.25s var(--animation-easing-function) !important;
  }
}

@include Option("userChrome.combined.urlbar_with_reload") {
  #nav-bar-customization-target > #stop-reload-button .toolbarbutton-icon {
    transition: background-color 2.5s var(--animation-easing-function) !important;
    &:hover {
      transition: background-color 1.25s var(--animation-easing-function) !important;
    }
  }
}

/*- Border - Other Fields --------------------------------------------------*/
#search-box,
xul|search-textbox.tabsFilter,
#editBMPanel_namePicker,
#editBMPanel_tagsField,
.findbar-container .findbar-textbox {
  transition: border-color 1s var(--animation-easing-function) !important;
  &:hover {
    transition: border-color 0.5s var(--animation-easing-function) !important;
  }
}

/*- Sidebar ----------------------------------------------------------------*/
@include NotOption("userChrome.decoration.disable_sidebar_animate") {
  #sidebar-box {
    /* like #sidebar-box > #sidebar */
    min-width: 14em;
    width: 18em;
    max-width: 36em;

    /* Animation */
    transition: margin-inline-start 0.25s var(--animation-easing-function), opacity 0.25s ease-in-out,
      visibility 0s linear !important;
    will-change: margin-inline-start, opacity, visibility;

    &[hidden="true"] {
      @include Box(true);
      margin-inline-start: -18em;
      opacity: 0;
      visibility: collapse;
      transition-delay: 0s, 0s, 0.25s !important;
    }
  }
}

/*- Titlebar & Full Screen -------------------------------------------------*/
#titlebar {
  will-change: background-color !important;
  transition: $toolbox-transition-background-color !important;

  &:-moz-window-inactive {
    transition: background-color 0.5s var(--animation-easing-function) !important;
  }
}
#navigator-toolbox {
  /* Full screen out */
  will-change: margin-top, background-color !important;
  transition: $toolbox-transition-margin-top,
              $toolbox-transition-background-color !important;
  transform-origin: top;

  &:-moz-window-inactive {
    transition: $toolbox-transition-margin-top,
                $toolbox-transition-background-color-inactive !important;
  }

  &[inFullscreen="true"] {
    /* Full screen enter */
    animation-duration: 1s;
    animation-name: fullscreen;
    animation-timing-function: ease;

    /* Full screen navbar not hover */
    // transition: margin-top 0.3s var(--animation-easing-function) 50ms;
    transition: $toolbox-transition-margin-top-fullscreen,
                $toolbox-transition-background-color !important;
    &:-moz-window-inactive {
      transition: $toolbox-transition-margin-top-fullscreen,
                  $toolbox-transition-background-color-inactive !important;
    }

    &:hover {
    // Full screen navbar hover
    // transition-duration: 1.5s; // Not works, because !important
    // transition-delay: 0.5s;
      margin-top: 0 !important;
    }
  }
}

@keyframes fullscreen {
  from {
    margin-top: 0;
  }
  /* Don't use `to`: Depending on density */
}

/*- Expand - Synced Tabs ---------------------------------------------------*/
@include moz-document(url "chrome://browser/content/syncedtabs/sidebar.xhtml") {
  .item-tabs-list {
    transition: transform 0.2s ease-out, opacity 0.2s ease-out;
    transform: translateY(0%);
    opacity: 1;
    max-height: 100%;
  }

  .item.client.closed .item-tabs-list {
    display: flex !important;

    transition: transform 0.2s ease-out, opacity 0.2s ease-out,
      max-height 0.25s cubic-bezier(0.82, 0.085, 0.395, 0.895) 0.05s;
    visibility: hidden;
    transform: translateY(-100%);
    opacity: 0;
    max-height: 0;
  }
}

/*- Arrow - Synced Tabs ----------------------------------------------------*/
@include moz-document(url "chrome://browser/content/syncedtabs/sidebar.xhtml") {
  /* treechildren::-moz-tree-twisty: Can't apply */
  #template-container .item.client {
    .item-twisty-container {
      transition: transform 0.1s var(--animation-easing-function) !important;
    }

    &.closed .item-twisty-container {
      transform: rotate(-90deg);
      background-image: url("chrome://global/skin/icons/arrow-down-12.svg") !important;

      &:dir(rtl) {
        transform: rotate(90deg);
      }
    }
  }
}

/*- Arrow - Edit Bookmark Popup --------------------------------------------*/
#editBookmarkPanelRows .expander-up .button-icon,
#editBookmarkPanelRows .expander-down .button-icon {
  transition: transform 0.1s var(--animation-easing-function) !important;
}
#editBookmarkPanelRows .expander-up {
  list-style-image: url("chrome://global/skin/icons/arrow-down.svg") !important;
  .button-icon {
    transform: rotate(180deg);
  }
}