I don't know. It's so easy to just create a random Gmail address and forward email from it. Maybe this makes it easier, but Gmail is one of the few Google products that I feel pretty confident will be around for a long time.
One still has to enter a mobile number to sign up for that Google account. But the larger difference is, that account would still be a standalone email address, which just happens to forward to your main Gmail address. But Firefox Relay (and similar products, like AnonAddy and SimpleLogin) are alias services. The idea with these services is to create addresses that can be immediately blocked, if they get into the hands of spammers. I am a happy SimpleLogin customer, and have made as many as 200 addresses. AnonAddy is a great start too, for those that need unlimited addresses. Both allow responding from those addresses, while AnonAddy's count is less.
Yandex Mail [0] is a better choice for this than Gmail. It also asks for a phone number to validate, on sign up. But there's a box you can tick which says something like "I don't have a mobile phone" and then you can validate with a Captcha instead
decrypt|5 years ago
Normille|5 years ago
[0]https://mail.yandex.com
elliotlarson|5 years ago