ignore "originalTarget" only if it can't be serialized

nicegui/templates/index.html

@@ -83,9 +83,14 @@
           }
           else {
             for (let k in arg) {
-              // we filter it out because it's supported in Firefox only and doesn't exist in other browsers. Fixes #2469.
-              if(k == 'originalTarget')
-                continue;              
+              // ignore "Restricted" fields in Firefox (see #2469)
+              if (k == 'originalTarget') {
+                try {
+                  JSON.stringify(arg[k]);
+                } catch (e) {
+                  continue;
+                }
+              }
               if (event_args === null || event_args[i] === null || event_args[i].includes(k)) {
                 filtered[k] = arg[k];
               }