FirefoxでのWebextensionのインストールに失敗します

`about:debugging`から`一時的なアドオンを読み込む`をクリックし、manifest.jsonを選択すると`There was an
error during installation: Extension is invalid`とだけ表示されます

どうすれば良いのでしょうか?

manifest.json

```

    
    {
        "manifest_version": 2,
        "name": "Beastify",
        "version": 1.0,
    
        "description": "add a browser action icon to the toolbar. Click the button to choose a beast. The active tab's body content is then replaced with a picture of the choosen beast.",
        "icons": {
            "48": "icons/beasts-48.png"
        },
    
        "permissions": [
            "activeTab"
        ],
    
        "browser_action": {
            "default_icon": "icons/beasts-32.png",
            "default_title": "Beastify",
            "default_popup": "popup/choose_beast.html"
        },
    
        "web_accessible_resources": [
            "beasts/frog.jpg",
            "beasts/turtle.jpg",
            "beasts/snake.jpg"
        ]
    }
    
    
    
```
CC BY-SA 3.0
2016-09-30T14:16:04.813
29272
2016-10-07T06:04:39.057
5246
question
javascript json firefox
webextensionのインストールに失敗する
"version"は文字列で、"description"は132文字まで・・・。
CC BY-SA 3.0
2016-10-07T06:04:39.057
29410
2016-10-07T06:04:39.057
13291
29272
answer