fix setting new mode when unset

js/index.js

@@ -34,7 +34,7 @@ function restore_options() {
         }
       } else {
         result.mode = "light"
-        browser.storage.sync.set(mode)
+        browser.storage.sync.set({mode:result.mode})
       }
       document.head.appendChild(style)
     }

js/options.js

@@ -45,7 +45,7 @@ function restore_options() {
         }
       } else {
         result.mode = "light"
-        browser.storage.sync.set(mode)
+        browser.storage.sync.set({mode:result.mode})
       }
       document.head.appendChild(style)
     }