Firefox Relay (https://relay.firefox.com/ has just exited beta and now has a premium tier ($1/month) that gives you more than the 5 email aliases the free plan provides.
I’ve been a big proponent of paying for an email service like FastMail.com and buying your own domain so you have an unlimited number of email addresses available to you. But it requires some geek work to bring it all together. Services like SimpleLogin.com provide similar capabilities by generating unique email addresses for you and forwarding them to an address you specify when you sign up. Mozilla’s service isn’t all that different but it’s from Mozilla and it’s pretty cheap (right now…they say it’s a promotional price with no mention of when the price will go up), Still, it’s a worthwhile investment if you don’t feel like giving your precious personal email address out to various websites and newsletters.