This is not necessarily Firefox, but because reCAPTCHA is designed to be more frictionless if Google can identify the user.
If you have their tracking cookies, if you don't use a VPN, and if you block ads (which would have more tracking cookies), Google's certainty of who you are is higher, increasing the chance that you are a human.
Firefox's default settings, especially with the new Content Blocking features, are enough for reCAPTCHA to be less sure you're a human, and try to make you prove it more often.
So Google manages to sell a product (reCAPTCHA), show good intentions (bot-prevention), increase usage of Chrome (because it's a smoother experience through reCAPTCHA), and get more information on everyone.
Win x4
If you have their tracking cookies, if you don't use a VPN, and if you block ads (which would have more tracking cookies), Google's certainty of who you are is higher, increasing the chance that you are a human.
Firefox's default settings, especially with the new Content Blocking features, are enough for reCAPTCHA to be less sure you're a human, and try to make you prove it more often.
So Google manages to sell a product (reCAPTCHA), show good intentions (bot-prevention), increase usage of Chrome (because it's a smoother experience through reCAPTCHA), and get more information on everyone.
Win x4