第一回答：

最后我明白了。

First Answer:

Finally I got it.

对于Firefox OS，图标大小应该是 30 X 30 或 60 X 60 。

For Firefox OS the icon size should be of size 30 X 30 or 60 X 60.

对于Firefox Market，图标大小应为 128 X 128

For Firefox Market place the icon size should be 128 X 128

对于Firefox OS，应该提供没有投影和
的图标关闭以下尺寸的裁剪帆布：

For Firefox OS icons should be provided without a drop shadow and a close cropped canvas in the following sizes:

30 x 30
60 x 60

注意： Firefox Marketplace要求所有提交的应用至少包含一个至少128 x 128的图标。

Note: Firefox Marketplace requires all submitted apps to have a minimum of one icon that is at least 128 x 128.

参考： Firefox OS - 样式指南

我用di添加了所有图像在我的申请的文档中指定的维度。但它也没有用!!!

I added all images with the dimensions specified in the doc to my application. But it also not worked !!!

Atlast我在我的项目中添加了一个目录 img 并添加了图标给它。然后修改 manifest.webapp 文件，如：

Atlast I added a directory img to my project and added icons to it. Then modified the manifest.webapp file like:

"icons": {
    "128": "/img/Feed.png"
  }

它对我有用，我不知道它是否是一个bug。

It worked for me, I don't know whether it is a bug or not.