diff --git a/CREDITS b/CREDITS
index 944d2c5..a2cc636 100644
--- a/CREDITS
+++ b/CREDITS
@@ -42,6 +42,9 @@ W: https://www.reddit.com/user/Backseat-Driver/
 N: badprogramshere
 W: https://github.com/badprogramshere
 
+N: BPower0036
+W: https://github.com/BPower0036
+
 N: Burak Yigit Kaya
 E: ben@byk.im
 W: https://byk.im/
diff --git a/css/leptonChrome.css b/css/leptonChrome.css
index e72481d..7c2f73f 100644
--- a/css/leptonChrome.css
+++ b/css/leptonChrome.css
@@ -3643,22 +3643,23 @@
 /** Tab Bar UI ****************************************************************/
 /*= Tabs on Bottom ===========================================================*/
 @supports -moz-bool-pref("userChrome.tab.on_bottom") or -moz-bool-pref("userChrome.fullscreen.overlap") {
-  #navigator-toolbox {
+  /* Don't use display: flex at not fullscreen!! side effect #372 */
+  :root[sizemode="fullscreen"] #navigator-toolbox {
     display: flex !important;
     /* Needed for content to take up entire height, compatibility with tabs on bottom */
     flex-wrap: wrap;
   }
 
-  #titlebar,
-  #nav-bar,
-  #PersonalToolbar,
-  #tab-notification-deck,
-  #tab-notification-deck-template {
+  :root[sizemode="fullscreen"] #titlebar,
+  :root[sizemode="fullscreen"] #nav-bar,
+  :root[sizemode="fullscreen"] #PersonalToolbar,
+  :root[sizemode="fullscreen"] #tab-notification-deck,
+  :root[sizemode="fullscreen"] #tab-notification-deck-template {
     flex-basis: 100%;
   }
 
   /* -moz-default-appearance: -moz-window-titlebar */
-  #titlebar {
+  :root[sizemode="fullscreen"] #titlebar {
     -moz-appearance: none !important;
   }
 }
@@ -3668,11 +3669,15 @@
   /*= Tabbar - Move to bottom ==================================================*/
   #titlebar {
     order: 2;
+    /* When userChrome.fullscreen.overlap */
+    -moz-box-ordinal-group: 2;
     --tabs-navbar-shadow-size: 0px;
   }
 
   #tab-notification-deck {
     order: 2;
+    /* When userChrome.fullscreen.overlap */
+    -moz-box-ordinal-group: 2;
   }
 
   #TabsToolbar .titlebar-spacer {
@@ -3682,6 +3687,8 @@
   @supports -moz-bool-pref("userChrome.tab.on_bottom.above_bookmark") {
     #PersonalToolbar {
       order: 2;
+      /* When userChrome.fullscreen.overlap */
+      -moz-box-ordinal-group: 2;
     }
   }
   @supports not -moz-bool-pref("userChrome.tab.on_bottom.above_bookmark") {
@@ -6008,7 +6015,7 @@
 
     :not(menu, #ContentSelectDropdown, #context-navigation)
       > menupopup
-      > menuitem[type="checkbox"][checked="false"]
+      > menuitem[type="checkbox"]:not([checked="true"])
       > .menu-iconic-left {
       padding-inline-start: var(--context-menu-text-padding);
     }
diff --git a/docs/Restrictions.md b/docs/Restrictions.md
index 12427ff..910d0f7 100644
--- a/docs/Restrictions.md
+++ b/docs/Restrictions.md
@@ -63,6 +63,8 @@ The following code will cause extension panels fail to open and trying to open t
 ```
 Info: `#nav-bar` is [`toolbar`](https://udn.realityripple.com/docs/Archive/Mozilla/XUL/toolbar).
 
+Another `display: flex`'s side effect examples. [#368](https://github.com/black7375/Firefox-UI-Fix/issues/368) [#372](https://github.com/black7375/Firefox-UI-Fix/issues/372)
+
 ## Internals
 ### CSS Loading Order
 User CSS(`userChrome.css`, `userContent.css`) is usually loaded first.
diff --git a/src/icons/_layout_menu.scss b/src/icons/_layout_menu.scss
index ba14f04..dbb393a 100644
--- a/src/icons/_layout_menu.scss
+++ b/src/icons/_layout_menu.scss
@@ -87,7 +87,7 @@ menupopup:is(#context_sendTabToDevicePopupMenu, #context-sendpagetodevice-popup)
   }
   :not(menu, #ContentSelectDropdown, #context-navigation)
     > menupopup
-    > menuitem[type="checkbox"][checked="false"]
+    > menuitem[type="checkbox"]:not([checked="true"])
     > .menu-iconic-left {
     padding-inline-start: var(--context-menu-text-padding);
   }
diff --git a/src/tabbar/_index.scss b/src/tabbar/_index.scss
index c8ee31a..4b18055 100644
--- a/src/tabbar/_index.scss
+++ b/src/tabbar/_index.scss
@@ -1,19 +1,20 @@
 /*= Tabs on Bottom ===========================================================*/
 @include Option("userChrome.tab.on_bottom", "userChrome.fullscreen.overlap") {
-  #navigator-toolbox {
+  /* Don't use display: flex at not fullscreen!! side effect #372 */
+  :root[sizemode="fullscreen"] #navigator-toolbox {
     display: flex !important; /* Needed for content to take up entire height, compatibility with tabs on bottom */
     flex-wrap: wrap;
   }
-  #titlebar,
-  #nav-bar,
-  #PersonalToolbar,
-  #tab-notification-deck,
-  #tab-notification-deck-template {
+  :root[sizemode="fullscreen"] #titlebar,
+  :root[sizemode="fullscreen"] #nav-bar,
+  :root[sizemode="fullscreen"] #PersonalToolbar,
+  :root[sizemode="fullscreen"] #tab-notification-deck,
+  :root[sizemode="fullscreen"] #tab-notification-deck-template {
     flex-basis: 100%;
   }
 
   /* -moz-default-appearance: -moz-window-titlebar */
-  #titlebar {
+  :root[sizemode="fullscreen"] #titlebar {
     -moz-appearance: none !important;
   }
 }
diff --git a/src/tabbar/_tabs_on_bottom.scss b/src/tabbar/_tabs_on_bottom.scss
index acf3ed1..f197f8a 100644
--- a/src/tabbar/_tabs_on_bottom.scss
+++ b/src/tabbar/_tabs_on_bottom.scss
@@ -3,11 +3,13 @@ See the above repository for updates as well as full license text. */
 
 /*= Tabbar - Move to bottom ==================================================*/
 #titlebar{
-  order: 2;
+  order: 2; /* When userChrome.fullscreen.overlap */
+  -moz-box-ordinal-group: 2;
   --tabs-navbar-shadow-size: 0px;
 }
 #tab-notification-deck {
-  order: 2;
+  order: 2; /* When userChrome.fullscreen.overlap */
+  -moz-box-ordinal-group: 2;
 }
 
 #TabsToolbar .titlebar-spacer {
@@ -16,7 +18,8 @@ See the above repository for updates as well as full license text. */
 
 @include Option("userChrome.tab.on_bottom.above_bookmark") {
   #PersonalToolbar {
-    order: 2;
+    order: 2; /* When userChrome.fullscreen.overlap */
+    -moz-box-ordinal-group: 2;
   }
 }
 @include NotOption("userChrome.tab.on_bottom.above_bookmark") {