As a developer who has worked with reCAPTCHA in the past and as a diehard Firefox user, what likely happened here is a form of shadow banning.

You're moving too fast; your mouse and mouse clicks are "too good" to be human. Try solving the reCAPTCHA slower and you'll see wildly different results, or, purposely fail one reCAPTCHA to get easier ones.

reCAPTCHA tech is crazy; reCAPTCHAs are not simple web forms and Javascript, they're a sandboxed and monitored 'window' to a Google server. If you solve too many reCAPTCHAs too quickly (ie. when you are testing a web page, or are rotating your passwords on many websites) then Google's servers will try to rate limit you with slow animations and harder reCAPTCHAs.