diff --git a/src/other/firefox/common/parts/csd.css b/src/other/firefox/common/parts/csd.css
index 863d54cf..68b4f871 100644
--- a/src/other/firefox/common/parts/csd.css
+++ b/src/other/firefox/common/parts/csd.css
@@ -3,8 +3,30 @@
 @namespace xul url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
 
 /* Headerbar top border corners rounded */
-:root[tabsintitlebar]:not([inFullscreen]):not([sizemode="maximized"]) #nav-bar {
-	border-radius: env(-moz-gtk-csd-titlebar-radius) env(-moz-gtk-csd-titlebar-radius) 0 0 !important;
+:root[tabsintitlebar][sizemode="normal"]:not([gtktiledwindow="true"]) {
+  #nav-bar {
+    border-top-left-radius: 12px !important;
+    border-top-right-radius: 12px !important;
+  }
+
+  /* stylelint-disable-next-line media-query-no-invalid */
+  @media (-moz-bool-pref: "widget.gtk.rounded-bottom-corners.enabled") {
+    #nav-bar {
+      /* The body clip below covers this. */
+      border-radius: 0 !important;
+    }
+
+    body, dialog,
+    dialog::backdrop {
+      /* Use an uniform clip to allow WebRender to optimize it better */
+      border-radius: 12px !important;
+    }
+
+    window[role="dialog"] {
+      border-bottom-left-radius: 12px !important;
+      border-bottom-right-radius: 12px !important;
+    }
+  }
 }
 
 /* Window buttons: at least 1 button */
diff --git a/src/other/firefox/common/parts/dialogs.css b/src/other/firefox/common/parts/dialogs.css
index acc21420..2b6a0bc3 100644
--- a/src/other/firefox/common/parts/dialogs.css
+++ b/src/other/firefox/common/parts/dialogs.css
@@ -82,6 +82,7 @@ dialog[subdialog] {
 /* Buttons */
 .dialog-button-box {
 	display: flex !important;
+	background: none !important;
 	border-top: 1px solid var(--gnome-menu-border-color) !important;
 	padding: 3px !important;
 }
@@ -131,11 +132,11 @@ dialog[subdialog] {
 
 :root[dialogroot] select,
 :host(dialog) select {
-  background-image: url("chrome://global/skin/icons/arrow-down-12.svg") !important;
+	background-image: url("chrome://global/skin/icons/arrow-down-12.svg") !important;
 	background-color: #ffffff !important;
-  background-position: right 12px center !important;
-  background-repeat: no-repeat !important;
-  background-size: auto 12px !important;
+	background-position: right 12px center !important;
+	background-repeat: no-repeat !important;
+	background-size: auto 12px !important;
 	border: 1px solid var(--gnome-button-border-color) !important;
 	border-bottom-color: var(--gnome-button-border-accent-color) !important;
 	border-radius: 8px !important;
@@ -212,7 +213,7 @@ dialog[subdialog] {
 #editBookmarkPanelContent > hbox > input {
 	background-color: #666666 !important;
 }
-	
+
 #cancel-button,
 #print-button.primary {
 	box-shadow: var(--gnome-button-box-shadow) !important;