loadFrameScript()を使って任意のスクリプトをFrame側に注入
↓
Frame側でwindow.getSelection()などを実行
↓
MessageListenerを使って実行結果をChrome側に送信
https://www43.atwiki.jp/fxext/pages/53.html
https://developer.mozilla.org/ja/docs/User:wbamberg/e10s/Working_with_multiprocess_Firefox
https://developer.mozilla.org/ja/Firefox/Multiprocess_Firefox/Message_Manager
