[Tiksi]

I've used both firefox (dev edition) and chrome pretty evenly for a long time (work stuff in chrome, personal in ff), and I haven't noticed any more reCaptchas in firefox than I get in chrome. If you just started using firefox, I could see the extra captchas being due to having "too clean" of a browser, or a different browser that was never used before tripping some sort of anti malware or suspicious login system.

All just speculation, but I haven't noticed the same issue.

[eyegor]

This is exactly it. Modern recaptcha is "reputation" based. So if it fingerprint matches you against a known profile, you never see the captcha. One could argue that a residential ip block combined with a common browser should be sufficient to filter most bot traffic, but it's not exactly in googles interest to worry about non-chrome user experience.

[Czarcasm]

Well TIL. This gives me hope. I will put some time back into FF and see if there is an eventual drop in reCaptcha.