Try to pass the serializable list using Bundle.Serializable:
Bundle bundle = new Bundle();
bundle.putSerializable("value", all_thumbs);
intent.putExtras(bundle);
And in SomeClass Activity get it as:
Intent intent = this.getIntent();
Bundle bundle = intent.getExtras();
List<Thumbnail> thumbs=
(List<Thumbnail>)bundle.getSerializable("value");