Transparency is leaking from menu's border

### Describe the bug

I'm using [kwin-effects-better-blur-dx](https://github.com/xarblu/kwin-effects-better-blur-dx) to make the menu blurry on KDE. The transparency "leak" made it blur outside the menu.

### Expected behavior

_No response_

### Screenshots

### OS

Linux

### OS - Others

_No response_

### Firefox Version

140.7.0esr

### Distribution

- [ ] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [x] [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
- [ ] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [x] 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

kde-gtk-config is doing its gtk stuff

user.js setup

```javascript

// v8.7.5 Lepton-Photon-Style
// ** 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", true);

// 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", false); // Original, Photon
user_pref("userChrome.tab.color_like_toolbar", false); // Original, Photon

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

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

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

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

// 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.windows_maximized", true);
// user_pref("userChrome.compatibility.os.win11", true);

// == 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", false); // only for linux

// user_pref("userChrome.decoration.disable_panel_animate", true);
// user_pref("userChrome.decoration.disable_sidebar_animate", true);
// user_pref("userChrome.decoration.panel_button_separator", true);
// 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", false);
// 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);

// 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);
// 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); // 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", false);
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", true);
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

// ** Useful Options ***********************************************************
// Tab preview
// https://blog.nightly.mozilla.org/2024/02/06/a-preview-of-tab-previews-these-weeks-in-firefox-issue-153/
user_pref("browser.tabs.hoverPreview.enabled", true);

// Paste suggestion at urlbar
// https://blog.nightly.mozilla.org/2023/12/04/url-gonna-want-to-check-this-out-these-weeks-in-firefox-issue-150/
user_pref("browser.urlbar.clipboard.featureGate", true);

// Integrated calculator at urlbar
user_pref("browser.urlbar.suggest.calculator", true);

// Integrated unit convertor at urlbar
// user_pref("browser.urlbar.unitConversion.enabled", true);

// Draw in Titlebar
// user_pref("browser.tabs.drawInTitlebar", true);
// user_pref("browser.tabs.inTitlebar", 1); // Nightly, 96 Above

// Searchbar, Removed from settings starting with FF v122
// user_pref("browser.search.widget.inNavBar", true);

// Firefox view search
// https://blog.nightly.mozilla.org/2023/12/14/better-searching-in-firefox-to-close-out-2023-these-weeks-in-firefox-issue-151/
// user_pref("browser.firefox-view.search.enabled", true);
// user_pref("browser.firefox-view.virtual-list.enabled", true);

// Firefox screenshot
// https://blog.nightly.mozilla.org/2024/01/22/happy-new-year-these-weeks-in-firefox-issue-152/
// user_pref("screenshots.browser.component.enabled", true);

// ** Scrolling Settings *******************************************************
// == Only Sharpen Scrolling ===================================================
// Pref Value Original
/*
user_pref("mousewheel.min_line_scroll_amount", 10); // 5
user_pref("general.smoothScroll.mouseWheel.durationMinMS", 80); // 50
user_pref("general.smoothScroll.currentVelocityWeighting", "0.15"); // "0.25"
user_pref("general.smoothScroll.stopDecelerationWeighting", "0.6"); // "0.4"
*/

// == Smooth Scrolling ==========================================================
// ** Scrolling Options ********************************************************
// based on natural smooth scrolling v2 by aveyo
// this preset will reset couple extra variables for consistency
// Pref Value Original
/*
user_pref("apz.allow_zooming", true); /// true
user_pref("apz.force_disable_desktop_zooming_scrollbars", false); /// false
user_pref("apz.paint_skipping.enabled", true); /// true
user_pref("apz.windows.use_direct_manipulation", true); /// true
user_pref("dom.event.wheel-deltaMode-lines.always-disabled", true); /// false
user_pref("general.smoothScroll.currentVelocityWeighting", "0.12"); /// "0.25" <- 1. If scroll too slow, set to "0.15"
user_pref("general.smoothScroll.durationToIntervalRatio", 1000); /// 200
user_pref("general.smoothScroll.lines.durationMaxMS", 100); /// 150
user_pref("general.smoothScroll.lines.durationMinMS", 0); /// 150
user_pref("general.smoothScroll.mouseWheel.durationMaxMS", 100); /// 200
user_pref("general.smoothScroll.mouseWheel.durationMinMS", 0); /// 50
user_pref("general.smoothScroll.mouseWheel.migrationPercent", 100); /// 100
user_pref("general.smoothScroll.msdPhysics.continuousMotionMaxDeltaMS", 12); /// 120
user_pref("general.smoothScroll.msdPhysics.enabled", true); /// false
user_pref("general.smoothScroll.msdPhysics.motionBeginSpringConstant", 200); /// 1250
user_pref("general.smoothScroll.msdPhysics.regularSpringConstant", 200); /// 1000
user_pref("general.smoothScroll.msdPhysics.slowdownMinDeltaMS", 10); /// 12
user_pref("general.smoothScroll.msdPhysics.slowdownMinDeltaRatio", "1.20"); /// "1.3"
user_pref("general.smoothScroll.msdPhysics.slowdownSpringConstant", 1000); /// 2000
user_pref("general.smoothScroll.other.durationMaxMS", 100); /// 150
user_pref("general.smoothScroll.other.durationMinMS", 0); /// 150
user_pref("general.smoothScroll.pages.durationMaxMS", 100); /// 150
user_pref("general.smoothScroll.pages.durationMinMS", 0); /// 150
user_pref("general.smoothScroll.pixels.durationMaxMS", 100); /// 150
user_pref("general.smoothScroll.pixels.durationMinMS", 0); /// 150
user_pref("general.smoothScroll.scrollbars.durationMaxMS", 100); /// 150
user_pref("general.smoothScroll.scrollbars.durationMinMS", 0); /// 150
user_pref("general.smoothScroll.stopDecelerationWeighting", "0.6"); /// "0.4"
user_pref("layers.async-pan-zoom.enabled", true); /// true
user_pref("layout.css.scroll-behavior.spring-constant", "250.0"); /// "250.0"
user_pref("mousewheel.acceleration.factor", 3); /// 10
user_pref("mousewheel.acceleration.start", -1); /// -1
user_pref("mousewheel.default.delta_multiplier_x", 100); /// 100
user_pref("mousewheel.default.delta_multiplier_y", 100); /// 100
user_pref("mousewheel.default.delta_multiplier_z", 100); /// 100
user_pref("mousewheel.min_line_scroll_amount", 0); /// 5
user_pref("mousewheel.system_scroll_override.enabled", true); /// true <- 2. If scroll too fast, set to false
user_pref("mousewheel.system_scroll_override_on_root_content.enabled", false); /// true
user_pref("mousewheel.transaction.timeout", 1500); /// 1500
user_pref("toolkit.scrollbox.horizontalScrollDistance", 4); /// 5
user_pref("toolkit.scrollbox.verticalScrollDistance", 3); /// 3

```

### Additional context

I know is wrong to have both `userChrome.tab.dynamic_separator` and `userChrome.tab.static_separator` enabled at the same time but it was the only way i found to remove this separator line:

Reproduce the issue on Linux with KDE, Firefox 140.7.0esr, Lepton's photon style, and userChrome.theme.transparent.menu enabled. Start by investigating the menu transparency behavior and the interaction with kwin-effects-better-blur-dx; done means the blur no longer appears outside the menu border.

Written by the indexing model from the issue text.