custom_err.diff

diff --git a/testing/geckodriver/marionette/src/result.rs b/testing/geckodriver/marionette/src/result.rs
index 72fec8d67cba..3b04217a4c20 100644
--- a/testing/geckodriver/marionette/src/result.rs
+++ b/testing/geckodriver/marionette/src/result.rs
@@ -1,4 +1,4 @@
-use serde::{Deserialize, Deserializer, Serialize, Serializer};
+use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 use serde_json::Value;
 
 use crate::common::{Cookie, Timeouts, WebElement};
@@ -71,7 +71,11 @@ where
         value: T,
     }
 
-    let w = Wrapper::deserialize(deserializer)?;
+    let v = Value::deserialize(deserializer)?;
+    dbg!(&v);
+
+    let w = serde_json::from_value::<Wrapper<T>>(v)
+        .map_err(de::Error::custom)?;
     Ok(w.value)
 }