diff --git a/components/malloc_size_of/lib.rs b/components/malloc_size_of/lib.rs
index a305f86f7cb..d65f8e957e4 100644
--- a/components/malloc_size_of/lib.rs
+++ b/components/malloc_size_of/lib.rs
@@ -777,12 +777,6 @@ impl<Impl: selectors::parser::SelectorImpl> MallocSizeOf
     }
 }
 
-impl MallocSizeOf for selectors::context::QuirksMode {
-    fn size_of(&self, _ops: &mut MallocSizeOfOps) -> usize {
-        0
-    }
-}
-
 impl MallocSizeOf for Void {
     #[inline]
     fn size_of(&self, _ops: &mut MallocSizeOfOps) -> usize {