There is already! However, depending on how long you've been a user, you might not see it yet; there's an option to allow us to store that data on our servers that we didn't turn on for people who were using Relay before that setting was introduced. You can enable it here ("Allow Relay to collect data showing the sites on which your masks are created and used"): https://relay.firefox.com/accounts/settings/
If you use the extension [1] [2], it can also store them locally if you want, and it will automatically track where you used the addresses, rather than you having to manually label them.
And finally, if you have Relay Premium, you can claim your own subdomain, and come up with an arbitrary address name (e.g. "hackernews@yourdomain.mozmail.com"), but since that's less anonymous than a random address, we recommend only using that if you need to come up with an address on the spot in the real world.
If you use the extension [1] [2], it can also store them locally if you want, and it will automatically track where you used the addresses, rather than you having to manually label them.
And finally, if you have Relay Premium, you can claim your own subdomain, and come up with an arbitrary address name (e.g. "hackernews@yourdomain.mozmail.com"), but since that's less anonymous than a random address, we recommend only using that if you need to come up with an address on the spot in the real world.
[1] https://addons.mozilla.org/firefox/addon/private-relay/
[2] https://chrome.google.com/webstore/detail/firefox-relay/lknp...