diff --git a/css/leptonContent.css b/css/leptonContent.css
index 02ccc11..910320f 100644
--- a/css/leptonContent.css
+++ b/css/leptonContent.css
@@ -2935,6 +2935,15 @@
       border-radius: 0 !important;
     }
   }
+  @-moz-document url-prefix("about:firefoxview") {
+    .card,
+    .card::before,
+    .empty-container,
+    .synced-tab-a,
+    .synced-tab-li-placeholder {
+      border-radius: 0 !important;
+    }
+  }
 }
 @-moz-document url-prefix("about:"), regexp(".*.pdf$") {
   @supports -moz-bool-pref("userChrome.rounding.square_dialog") {
diff --git a/src/contents/_rounding.scss b/src/contents/_rounding.scss
index 7b59098..1056498 100644
--- a/src/contents/_rounding.scss
+++ b/src/contents/_rounding.scss
@@ -169,4 +169,14 @@
       border-radius: 0 !important;
     }
   }
+
+  @include moz-document(url-prefix "about:firefoxview") {
+    .card,
+    .card::before, // .zap-card border
+    .empty-container,
+    .synced-tab-a,
+    .synced-tab-li-placeholder {
+      border-radius: 0 !important;
+    }
+  }
 }