Comment # 3 on bug 1231648 from simon becherer

Did not know if this is useful:

extras/developer-tools/errorconsole:

did an output when it should open encrypted attachments:

NS_BASE_STREAM_CLOSED: Component returned failure code: 0x80470002
(NS_BASE_STREAM_CLOSED) [nsIInputStream.available] NetUtil.sys.mjs:445
    readInputStream resource://gre/modules/NetUtil.sys.mjs:445
    buffer resource:///modules/AttachmentInfo.sys.mjs:214
    onStopRequest resource://gre/modules/NetUtil.sys.mjs:124