"Sidebar Overlap" is broken again

### Describe the bug

After Firefox 138/139 upgrades sidebar overlapping is broken again, same way I've described in my previous report #1052 .

### Expected behavior

_No response_

### Screenshots


### OS

Windows 11

### OS - Others

_No response_

### Firefox Version

139.0.1

### Distribution

- [x] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [ ] [Lepton's photon style](https://github.com/black7375/Firefox-UI-Fix/tree/photon-style)
- [ ] [Lepton's proton style](https://github.com/black7375/Firefox-UI-Fix/tree/proton-style)

### Theme

- [ ] Light
- [x] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [ ] System Default
- [ ] Others: (e.g. [Photon Colors](https://addons.mozilla.org/en-US/firefox/addon/photon-colors/), [Google Chrome Dark](https://addons.mozilla.org/en-US/firefox/addon/google-chrome-dark/), [Fairytale Of Nature](https://addons.mozilla.org/en-US/firefox/addon/fairytale-of-nature/))

### Theme - More Info

_No response_

### `user.js` setup

user.js setup

```javascript
// LEPTON v8.7.1

// ** Theme Default Options ****************************************************
// userchrome.css usercontent.css activate
user_pref("toolkit.legacyUserProfileCustomizations.stylesheets", true);

// Fill SVG Color
user_pref("svg.context-properties.content.enabled", true);

// Restore Compact Mode - 89 Above
user_pref("browser.compactmode.show", true);

// about:home Search Bar - 89 Above
user_pref("browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar", false);

// CSS's `:has()` selector #457 - 103 Above
user_pref("layout.css.has-selector.enabled", true);

// Browser Theme Based Scheme - Will be activate 95 Above
// user_pref("layout.css.prefers-color-scheme.content-override", 3);

// ** Theme Related Options ****************************************************
// == Theme Distribution Settings ==============================================
// The rows that are located continuously must be changed `true`/`false` explicitly because there is a collision.
// https://github.com/black7375/Firefox-UI-Fix/wiki/Options#important
user_pref("userChrome.tab.connect_to_window", true); // Original, Photon
user_pref("userChrome.tab.color_like_toolbar", true); // Original, Photon

user_pref("userChrome.tab.lepton_like_padding", true); // Original
user_pref("userChrome.tab.photon_like_padding", false); // Photon

user_pref("userChrome.tab.dynamic_separator", true); // Original, Proton
user_pref("userChrome.tab.static_separator", false); // Photon
user_pref("userChrome.tab.static_separator.selected_accent", false); // Just option
user_pref("userChrome.tab.bar_separator", false); // Just option

user_pref("userChrome.tab.newtab_button_like_tab", true); // Original
user_pref("userChrome.tab.newtab_button_smaller", false); // Photon
user_pref("userChrome.tab.newtab_button_proton", false); // Proton

user_pref("userChrome.icon.panel_full", true); // Original, Proton
user_pref("userChrome.icon.panel_photon", false); // Photon

// Original Only
user_pref("userChrome.tab.box_shadow", true);
user_pref("userChrome.tab.bottom_rounded_corner", true);

// Photon Only
user_pref("userChrome.tab.photon_like_contextline", false);
user_pref("userChrome.rounding.square_tab", false);

// Proton Only
// user_pref("userChrome.tab.supernova_like_contextline", true);

// == Theme Compatibility Settings =============================================
// user_pref("userChrome.compatibility.accent_color", true); // Firefox v103 Below
// user_pref("userChrome.compatibility.covered_header_image", true);
// user_pref("userChrome.compatibility.panel_cutoff", true);
// user_pref("userChrome.compatibility.navbar_top_border", true);
// user_pref("userChrome.compatibility.dynamic_separator", true); // Need dynamic_separator

// user_pref("userChrome.compatibility.os.linux_non_native_titlebar_button", true);
// user_pref("userChrome.compatibility.os.windows_maximized", true);
user_pref("userChrome.compatibility.os.win11", true); ///// ENABLED BY ME /////

// == Theme Custom Settings ====================================================
// -- User Chrome --------------------------------------------------------------
// user_pref("userChrome.theme.private", true);
// user_pref("userChrome.theme.proton_color.dark_blue_accent", true);
// user_pref("userChrome.theme.monospace", true);
// user_pref("userChrome.theme.transparent.frame", true);
// user_pref("userChrome.theme.transparent.menu", true);
// user_pref("userChrome.theme.transparent.panel", true);
// user_pref("userChrome.theme.non_native_menu", true); // only for linux

// user_pref("userChrome.decoration.disable_panel_animate", true);
user_pref("userChrome.decoration.disable_sidebar_animate", true); ///// ENABLED BY ME /////
user_pref("userChrome.decoration.panel_button_separator", true); ///// ENABLED BY ME /////
// user_pref("userChrome.decoration.panel_arrow", true);

// user_pref("userChrome.autohide.tab", true);
// user_pref("userChrome.autohide.tab.opacity", true);
// user_pref("userChrome.autohide.tab.blur", true);
// user_pref("userChrome.autohide.tabbar", true);
// user_pref("userChrome.autohide.navbar", true);
// user_pref("userChrome.autohide.bookmarkbar", true);
// user_pref("userChrome.autohide.sidebar", true);
// user_pref("userChrome.autohide.fill_urlbar", true);
// user_pref("userChrome.autohide.back_button", true);
// user_pref("userChrome.autohide.forward_button", true);
// user_pref("userChrome.autohide.page_action", true);
// user_pref("userChrome.autohide.toolbar_overlap", true);
// user_pref("userChrome.autohide.toolbar_overlap.allow_layout_shift", true);

// user_pref("userChrome.hidden.tab_icon", true);
// user_pref("userChrome.hidden.tab_icon.always", true);
// user_pref("userChrome.hidden.tabbar", true);
// user_pref("userChrome.hidden.navbar", true);
// user_pref("userChrome.hidden.private_indicator", true);
// user_pref("userChrome.hidden.titlebar_container", true);
// user_pref("userChrome.hidden.sidebar_header", true);
// user_pref("userChrome.hidden.sidebar_header.vertical_tab_only", true);
// user_pref("userChrome.hidden.urlbar_iconbox", true);
// user_pref("userChrome.hidden.urlbar_iconbox.label_only", true);
// user_pref("userChrome.hidden.bookmarkbar_icon", true);
// user_pref("userChrome.hidden.bookmarkbar_label", true);
// user_pref("userChrome.hidden.disabled_menu", true);

// user_pref("userChrome.centered.tab", true);
// user_pref("userChrome.centered.tab.label", true);
// user_pref("userChrome.centered.urlbar", true);
// user_pref("userChrome.centered.bookmarkbar", true);

// user_pref("userChrome.counter.tab", true);
// user_pref("userChrome.counter.bookmark_menu", true);

// user_pref("userChrome.combined.nav_button", true);
// user_pref("userChrome.combined.nav_button.home_button", true);
// user_pref("userChrome.combined.urlbar.nav_button", true);
// user_pref("userChrome.combined.urlbar.home_button", true);
// user_pref("userChrome.combined.urlbar.reload_button", true);
// user_pref("userChrome.combined.sub_button.none_background", true);
// user_pref("userChrome.combined.sub_button.as_normal", true);

// user_pref("userChrome.rounding.square_button", true);
// user_pref("userChrome.rounding.square_dialog", true);
// user_pref("userChrome.rounding.square_panel", true);
// user_pref("userChrome.rounding.square_panelitem", true);
// user_pref("userChrome.rounding.square_menupopup", true);
// user_pref("userChrome.rounding.square_menuitem", true);
// user_pref("userChrome.rounding.square_infobox", true);
// user_pref("userChrome.rounding.square_toolbar", true);
// user_pref("userChrome.rounding.square_field", true);
// user_pref("userChrome.rounding.square_urlView_item", true);
// user_pref("userChrome.rounding.square_checklabel", true);

// user_pref("userChrome.padding.first_tab", true);
// user_pref("userChrome.padding.first_tab.always", true);
// user_pref("userChrome.padding.drag_space", true);
// user_pref("userChrome.padding.drag_space.maximized", true);

// user_pref("userChrome.padding.toolbar_button.compact", true);
// user_pref("userChrome.padding.menu_compact", true);
// user_pref("userChrome.padding.bookmark_menu.compact", true);
// user_pref("userChrome.padding.urlView_expanding", true);
// user_pref("userChrome.padding.urlView_result", true);
// user_pref("userChrome.padding.panel_header", true);

// user_pref("userChrome.urlbar.iconbox_with_separator", true);

// user_pref("userChrome.urlView.as_commandbar", true);
// user_pref("userChrome.urlView.full_width_padding", true);
// user_pref("userChrome.urlView.always_show_page_actions", true);
// user_pref("userChrome.urlView.move_icon_to_left", true);
// user_pref("userChrome.urlView.go_button_when_typing", true);
// user_pref("userChrome.urlView.focus_item_border", true);

// user_pref("userChrome.tabbar.as_titlebar", true);
// user_pref("userChrome.tabbar.fill_width", true);
// user_pref("userChrome.tabbar.multi_row", true);
// user_pref("userChrome.tabbar.unscroll", true);
// user_pref("userChrome.tabbar.on_bottom", true);
// user_pref("userChrome.tabbar.on_bottom.above_bookmark", true); // Need on_bottom
// user_pref("userChrome.tabbar.on_bottom.menubar_on_top", true); // Need on_bottom
// user_pref("userChrome.tabbar.on_bottom.hidden_single_tab", true); // Need on_bottom
// user_pref("userChrome.tabbar.one_liner", true);
// user_pref("userChrome.tabbar.one_liner.combine_navbar", true); // Need one_liner
// user_pref("userChrome.tabbar.one_liner.tabbar_first", true); // Need one_liner
// user_pref("userChrome.tabbar.one_liner.responsive", true); // Need one_liner

// user_pref("userChrome.tab.bottom_rounded_corner.all", true);
// user_pref("userChrome.tab.bottom_rounded_corner.australis", true);
// user_pref("userChrome.tab.bottom_rounded_corner.edge", true);
// user_pref("userChrome.tab.bottom_rounded_corner.chrome", true);
// user_pref("userChrome.tab.bottom_rounded_corner.chrome_legacy", true);
// user_pref("userChrome.tab.bottom_rounded_corner.wave", true);
// user_pref("userChrome.tab.always_show_tab_icon", true);
// user_pref("userChrome.tab.close_button_at_pinned", true);
// user_pref("userChrome.tab.close_button_at_pinned.always", true);
// user_pref("userChrome.tab.close_button_at_pinned.background", true);
// user_pref("userChrome.tab.close_button_at_hover.always", true); // Need close_button_at_hover
// user_pref("userChrome.tab.close_button_at_hover.with_selected", true); // Need close_button_at_hover
// user_pref("userChrome.tab.sound_show_label", true); // Need remove sound_hide_label
// user_pref("userChrome.tab.container.on_top", true);
// user_pref("userChrome.tab.container.always_long", true);
// user_pref("userChrome.tab.sound_with_favicons.on_center", true);
// user_pref("userChrome.tab.selected_bold", true);

// user_pref("userChrome.navbar.as_sidebar", true);

// user_pref("userChrome.bookmarkbar.multi_row", true);

user_pref("userChrome.findbar.floating_on_top", true); ///// ENABLED BY ME /////

// user_pref("userChrome.panel.remove_strip", true);
// user_pref("userChrome.panel.full_width_separator", true);
// user_pref("userChrome.panel.full_width_padding", true);

// user_pref("userChrome.sidebar.overlap", true);

// user_pref("userChrome.icon.disabled", true);
// user_pref("userChrome.icon.account_image_to_right", true);
// user_pref("userChrome.icon.account_label_to_right", true);
user_pref("userChrome.icon.menu.full", true); ///// ENABLED BY ME /////
// user_pref("userChrome.icon.global_menu.mac", true);

// -- User Content -------------------------------------------------------------
// user_pref("userContent.player.ui.twoline", true);

// user_pref("userContent.newTab.hidden_logo", true);
user_pref("userContent.newTab.background_image", true); ///// ENABLED BY ME ///// Need wallpaper image to `userContent.css`. :root { --uc-newTab-wallpaper: url("../icons/background_image.png"); }

// user_pref("userContent.page.proton_color.dark_blue_accent", true);
// user_pref("userContent.page.proton_color.system_accent", true);
// user_pref("userContent.page.dark_mode.pdf", true);
// user_pref("userContent.page.monospace", true);

// == Theme Default Settings ===================================================
// -- User Chrome --------------------------------------------------------------
user_pref("userChrome.compatibility.theme", true);
user_pref("userChrome.compatibility.os", true);

user_pref("userChrome.theme.built_in_contrast", true);
user_pref("userChrome.theme.system_default", true);
user_pref("userChrome.theme.proton_color", true);
user_pref("userChrome.theme.proton_chrome", true); // Need proton_color
user_pref("userChrome.theme.fully_color", true); // Need proton_color
user_pref("userChrome.theme.fully_dark", true); // Need proton_color

user_pref("userChrome.decoration.cursor", true);
user_pref("userChrome.decoration.field_border", true);
user_pref("userChrome.decoration.download_panel", true);
user_pref("userChrome.decoration.animate", true);

user_pref("userChrome.padding.tabbar_width", true);
user_pref("userChrome.padding.tabbar_height", true);
user_pref("userChrome.padding.toolbar_button", true);
user_pref("userChrome.padding.navbar_width", true);
user_pref("userChrome.padding.urlbar", true);
user_pref("userChrome.padding.bookmarkbar", true);
user_pref("userChrome.padding.infobar", true);
user_pref("userChrome.padding.menu", true);
user_pref("userChrome.padding.bookmark_menu", true);
user_pref("userChrome.padding.global_menubar", true);
user_pref("userChrome.padding.panel", true);
user_pref("userChrome.padding.popup_panel", true);

user_pref("userChrome.tab.multi_selected", true);
user_pref("userChrome.tab.unloaded", true);
user_pref("userChrome.tab.letters_cleary", true);
user_pref("userChrome.tab.close_button_at_hover", true);
user_pref("userChrome.tab.sound_hide_label", true);
user_pref("userChrome.tab.sound_with_favicons", true);
user_pref("userChrome.tab.pip", true);
user_pref("userChrome.tab.container", true);
user_pref("userChrome.tab.crashed", true);

user_pref("userChrome.fullscreen.overlap", false); ///// Disabled to fix URL bar highlighting /////
user_pref("userChrome.fullscreen.show_bookmarkbar", true);

user_pref("userChrome.icon.library", true);
user_pref("userChrome.icon.panel", true);
user_pref("userChrome.icon.menu", true);
user_pref("userChrome.icon.context_menu", true);
user_pref("userChrome.icon.global_menu", true);
user_pref("userChrome.icon.global_menubar", true);
user_pref("userChrome.icon.1-25px_stroke", true);

// -- User Content -------------------------------------------------------------
user_pref("userContent.player.ui", true);
user_pref("userContent.player.icon", true);
user_pref("userContent.player.noaudio", true);
user_pref("userContent.player.size", true);
user_pref("userContent.player.click_to_play", true);
user_pref("userContent.player.animate", true);

user_pref("userContent.newTab.full_icon", true);
user_pref("userContent.newTab.animate", true);
user_pref("userContent.newTab.pocket_to_last", true);
user_pref("userContent.newTab.searchbar", true);

user_pref("userContent.page.field_border", true);
user_pref("userContent.page.illustration", true);
user_pref("userContent.page.proton_color", true);
user_pref("userContent.page.dark_mode", true); // Need proton_color
user_pref("userContent.page.proton", true); // Need proton_color

// OTHER

// Move to New Window in the Tab Context Menu fix for TabMixPlus
user_pref("extensions.tabmix.detachTabMenu", true);
```

### Additional context

_No response_

Reproduce the overlap on Windows 11 with Firefox 139.0.1, the Original Lepton distribution, dark theme, and the supplied user.js setup. Compare the result with previous report #1052 and the screenshot; done means the sidebar no longer overlaps after the regression is addressed.

Written by the indexing model from the issue text.