Recently I've started having trouble passing Cloudflare captcha in Firefox - see below:

After playing around with extensions, I've realised that JavaScript Error Notifier is actually to blame.

Repro:
Have Firefox with no extensions in private mode, go to https://dash.cloudflare.com/login - captcha works.
Install JavaScript Errors Notifier, go to the same page - captcha breaks and goes into a frenzied loop