"NS_ERROR_NOT_AVAILABLE" error opening HTML with JS script inside GeckoView

Question

I'm trying to make an Android app that shows the content of an HTML using GeckoView

//MainActivity.kt

class MainActivity : AppCompatActivity() {
    private lateinit var geckoView: GeckoView
    private val geckoSession = GeckoSession(GeckoSessionSettings.Builder().allowJavascript(true).build())

    private fun setupGeckoView() {
        // 1
        geckoView = findViewById(R.id.geckoview)

        // 2
        val runtime = GeckoRuntime.create(this)
        geckoSession.open(runtime)

        // 3
        geckoView.setSession(geckoSession)

        // 4
        val apkURI: URI = File(packageResourcePath).toURI()
        val assetsURL = "jar:$apkURI!/assets/"
        val myURL = assetsURL + "index.html"
        geckoSession.loadUri(myURL)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        setupGeckoView()
    }
}

In the assets I have the index.html, a bunch of .css and a .js script. The app launches, correctly displays the html (meaning that also css was correctly loaded), but the js script doesnt start and this error is returned:

[JavaScript Error: "NS_ERROR_NOT_AVAILABLE: " {file: "jar:file:///data/app/com.icp.firefox_app-2/base.apk!/assets/full-offline.iife.js" line: 3}]
                                                                                                    @jar:file:///data/app/com.icp.firefox_app-2/base.apk!/assets/full-offline.iife.js:3:4777
                                                                                                    @jar:file:///data/app/com.icp.firefox_app-2/base.apk!/assets/full-offline.iife.js:101937:101768

Doesn anyone have any idea what could be the problem?