karma-firefox-launcher: Firefox 68.x won't run (from inside docker)

I’ve used FirefoxHeadless inside docker just fine for a long time - but with v68 of ffox it just won’t work.

19:02:46 09 08 2019 17:02:44.991:INFO [launcher]: Starting browser FirefoxHeadless
19:03:54 09 08 2019 17:03:45.123:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing.
19:03:54 09 08 2019 17:03:45.598:INFO [launcher]: Trying to start FirefoxHeadless again (1/2).
19:04:54 09 08 2019 17:04:45.602:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing.
19:04:54 09 08 2019 17:04:45.724:INFO [launcher]: Trying to start FirefoxHeadless again (2/2).
19:05:50 09 08 2019 17:05:45.855:WARN [launcher]: FirefoxHeadless have not captured in 60000 ms, killing.
19:05:50 09 08 2019 17:05:47.109:ERROR [launcher]: FirefoxHeadless failed 2 times (timeout). Giving up.

Karma config:

// Karma configuration file, see link for more information
// https://karma-runner.github.io/0.13/config/configuration-file.html

//https://hackernoon.com/running-karma-tests-with-headless-chrome-inside-docker-ae4aceb06ed3
const isDocker = require('is-docker')();


module.exports = function (config) {
  config.set({
    concurrency: 1, // avoid clash when ffox and chrome run at the same time
    customLaunchers: {
      ChromeCustom: {
        base: 'ChromeHeadless',
        // We must disable the Chrome sandbox when running Chrome inside Docker (Chrome's sandbox needs
        // more permissions than Docker allows by default)
        flags: isDocker ? ['--no-sandbox'] : []
      }
    },
    basePath: '',
    frameworks: ['jasmine', '@angular-devkit/build-angular'],
    plugins: [
      require('karma-jasmine'),
      require('karma-coverage'),
      require('karma-coverage-istanbul-reporter'),
      require('karma-chrome-launcher'),
      require('karma-firefox-launcher'),
      require('karma-junit-reporter'),
      //require('karma-remap-istanbul'),
      require('@angular-devkit/build-angular/plugins/karma')
    ],
    files: [
    ],
    preprocessors: {
      './src/app/**/*.ts': ['coverage']
    },
    coverageReporter: {
      type:'lcov',
      dir:'target/coverage'
    },
    mime: {
      'text/x-typescript': ['ts','tsx']
    },
    angularCli: {
      config: './angular-cli.json',
      environment: 'dev'
    },
    reporters: config.angularCli && config.angularCli.codeCoverage
              ? ['progress', 'junit','coverage-istanbul','coverage']
              : ['progress', 'junit'],
    junitReporter: {
      outputDir: 'target/junit-reports'
      //outputDir: 'target/junit-dir: require('path').join(__dirname, 'coverage'), reports'
    },
    port: 9876,
    colors: true,
    autoWatch: true,
    browsers: ['FirefoxHeadless','ChromeCustom'],
    singleRun: false
  });
};

Image I am using: https://hub.docker.com/r/evryfs/node-dev-docker/ (node12 tag)