Having used Todoist for Firefox since january, I'm quite happy. The only feature I missed was the integration with GMail, but I discovered that adding e-mails was still possible via the actual extension pop-out itself (when the e-mail is open).
That doesn't provide me with the button in GMail, but I really don't need that.

Besides that, it works great in 57, and I use Todoist so much that I can't imagine not having it.