Push Notifications (aka HTML5) prevent website start?!

Hi folks,

Whenever I add the HTML5 component to my setup the frontend (HTML interface) fails to start.

I’ve tried adding a package as follows:

notify:
  - name: html5
    platform: html5
    gcm_api_key: !secret gcm_api_key
    gcm_sender_id: !secret gcm_sender_id

I’ve also tried removing pushbullet and doing it in the configuration.yaml itself, tried it without gcm keys, and basically everything I could think of. I have all the requirements installed as per:

Does anyone have any advice on how to potentially troubleshoot this? The only thing I see in logs is:

[homeassistant.loader] Loaded notify.html5 from homeassistant.components.notify.html5#033[0m

No warnings/errors are logged.

Am I the only one trying to use this, the only one with the problem, or just unfortunate that no one is replying?