Why firefox addon has no valid entry point?

Question

I make Firefox addon using JPM, and when try to run it in dev mode:

jpm run -b $(which firefox)

have a message:

JPM [info] Starting jpm run on bgworker
JPM [error] Error: The addon has no valid entry point. Either create an entry point at `./index.js`, or set the `main` property to a valid path in your addon.

But in my addon xpi package exist ./index.js.

I even try to write

"main": "./index.js" 

in package.json.

I think there is no problem in my addon code but in my environment.

Using Xubuntu 15.10 x64, JPM 1.0.7.