My cat jumped on my keyboad and Firefox detected 'unusual activity' She probably hit a combination of keys which lead to said activity. Instantly, I had to verify whether I was a human. I did, but really, it was my cat. Neither my cat, nor myself have bad intentions. I just thought Firefox security should know that these things might happen.

I hope that my cat's activity didn't compromise my account. Maybe 'unusual activity' should be less strict, though I do understand that Firefox must be vigilant. Maybe it would be a good idea to let users describe what happened, before sending Captcha?