--- a/toolkit/components/places/PlacesTransactions.jsm
+++ b/toolkit/components/places/PlacesTransactions.jsm
@@ -732,18 +732,21 @@ function checkProperty(obj, prop, requir
 DefineTransaction.annotationObjectValidate = function(obj) {
   if (obj &&
       checkProperty(obj, "name", true, v => typeof(v) == "string" && v.length > 0) &&
       checkProperty(obj, "expires", false, Number.isInteger) &&
       checkProperty(obj, "flags", false, Number.isInteger) &&
       checkProperty(obj, "value", false, isPrimitive) ) {
     // Nothing else should be set
     let validKeys = ["name", "value", "flags", "expires"];
-    if (Object.keys(obj).every(k => validKeys.includes(k)))
-      return obj;
+    if (Object.keys(obj).every(k => validKeys.includes(k))) {
+      // Annotations objects are passed through to the backend, to avoid memory
+      // leaks, we must clone the object.
+      return {...obj};
+    }
   }
   throw new Error("Invalid annotation object");
 };
 
 DefineTransaction.childObjectValidate = function(obj) {
   if (obj &&
       checkProperty(obj, "title", false, v => typeof(v) == "string") &&
       !("type" in obj && obj.type != PlacesUtils.bookmarks.TYPE_BOOKMARK)) {