Firefox browser disconnect issue when running tests via testem

I am trying to run my ember tests in parallel using ember exam. However when I run the tests I am frequently getting browser disconnect issue, with following log:

[16:41:10][Step 6/6] not ok 561 Firefox - error
[16:41:10][Step 6/6]     ---
[16:41:10][Step 6/6]         message: >
[16:41:10][Step 6/6]             Error: Browser disconnected
[16:41:10][Step 6/6]             Stderr: 
[16:41:10][Step 6/6]              *** You are running in headless mode.
[16:41:10][Step 6/6]             [Parent 12706, Gecko_IOThread] WARNING: pipe error (45): Connection reset by peer: file /build/firefox-8HKHfQ/firefox-57.0+build4/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 353
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             ###!!! [Parent][MessageChannel] Error: (msgtype=0x24001F,name=PContent::Msg_PreferenceUpdate) Channel error: cannot send/recv
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             ###!!! [Parent][MessageChannel] Error: (msgtype=0x150083,name=PBrowser::Msg_Destroy) Channel error: cannot send/recv
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             ###!!! [Parent][MessageChannel] Error: (msgtype=0x150083,name=PBrowser::Msg_Destroy) Channel error: cannot send/recv
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]             
[16:41:10][Step 6/6]         Log: |
[16:41:10][Step 6/6]             { type: 'error', text: 'Error: Browser disconnected' }
[16:41:10][Step 6/6]             { type: 'error',
[16:41:10][Step 6/6]               text: '*** You are running in headless mode.\n[Parent 12706, Gecko_IOThread] WARNING: pipe error (45): Connection reset by peer: file /build/firefox-8HKHfQ/firefox-57.0+build4/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 353\n\n###!!! [Parent][MessageChannel] Error: (msgtype=0x24001F,name=PContent::Msg_PreferenceUpdate) Channel error: cannot send/recv\n\n\n###!!! [Parent][MessageChannel] Error: (msgtype=0x150083,name=PBrowser::Msg_Destroy) Channel error: cannot send/recv\n\n\n###!!! [Parent][MessageChannel] Error: (msgtype=0x150083,name=PBrowser::Msg_Destroy) Channel error: cannot send/recv\n\n' }
[16:41:10][Step 6/6]     ...

I am running firefox version 57, version 59 is better but even there I see this issue quite frequently, chrome however seems to fare well but on occasion it fails too. Initially I thought its because I am running in headless mode, but even in non-headless mode things do not get any better. And my testem.js file is:

let today = new Date();
const testWindowWidth = 1920;
const testWindowHeight = 1080;

/**
 * Exports configuration to run tests via testem.
 * There are issues with running the test in firefox in headless mode.
 * Chrome however works fine with the provided configuration.
 * @see : https://github.com/testem/testem/issues/1117
 * */
module.exports = {
    'framework': 'qunit',
    'test_page': [
        'tests/index.html?hidepassed&nojshint'
    ],
    'disable_watching': true,
    'parallel': -1,//sky is the limit
    'launch_in_ci': [
        'Firefox'
    ],
    'launch_in_dev': [
        'Chrome'
    ],
    'browser_args': {
        'Firefox': [
            `-headless`,//comment this line out for debugging purpose
            `-width ${testWindowWidth}`,
            `-height ${testWindowHeight}`
        ],
        'Chrome': [
            '--headless',//comment this line out for debugging purpose
            '--disable-gpu',
            '--remote-debugging-port=9222',
            '--remote-debugging-address=0.0.0.0',
            '--no-sandbox',
            '--user-data-dir=/tmp',
            `--window-size=${testWindowWidth},${testWindowHeight}`
        ]
    },
    'browser_start_timeout': 2 * 60,
    'report_file': `tests/logs/${today.getFullYear()}-${today.getMonth() + 1}-${today.getDate()}/${today}.txt`,
    'browser_disconnect_timeout': 2 * 60
};

I don't know if the problem is with testem configuration or the browser itself! Your help/suggestions will be much appreciated, thanks.