ReCAPTCHA is especially brutal if you aren't logged in to Google and are using Firefox. They make you do challenge after challenge after challenge and s-l-o-w-l-y fade in pictures as extra punishment. I've stopped using some sites because of it.
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
I mean, I have noticed those harder captures too since I switched to Firefox, but I didn't realize it was due to the different browser. I thought it was just a newer version.
I sometimes use Random User-Agent as well to resist fingerprinting; this makes ReCAPTCHA not just extremely tedious (up to about 10 rounds of sl-o-o-o-wly fading pictures) but literally impossible (it never ends).