Awesome idea, looks good!
It needs a way to select the alias quickly and insert it in forms. I'd say either make the alias customizable or make the plugin icon bar show the aliases with a small copy button near them.

Good work Mozilla!

A few features are left to be desired: The top bar icon would be more helpful if it showed the emails you've generated already; allowance of "-" in the url string. Every test environment on Netlify uses it. I would see relay as a great tool for registering test emails for developers.

I _want_ to like this, but there are some issues. In order for this service to be more useful than anonaddy, it needs to have the ability to create unlimited aliases with labels so that you can identify which are which.
Use Case: Using a different alias for each website so that you know which site leaked your email to other sites.

Being able to create an alias straight from the extension would be great as well. This would allow me to create an email alias with the firefox relay extension and the password with the lastpass extension. This pair would be a match made in heaven.

The ability to reply to emails that originated from Firefox Relay would also be a nice feature.

I'll be keeping an eye on this for future improvements. It definitely has potential.

I love it. It works as expected. 5 alias limit might seem too restrictive, but at the moment I am not impacted by it.
I miss two things
1. my own alias which many have reported
2. Change my forwarding email address. Right now it only takes email from firefox account.

Nov 1st, 2020;
Without the ability to reply using the Firefox relay alias, the very purpose to use Relay is moot!
I contacted a car dealership using one of my aliases. However, I had to reply using my own personal email, which got captured by the dealership, and I am now permanently entered in his distribution list.
So, what is the point?
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I would like to have the option to create my own prefix email, using the @relay.firefox.com. Without the limitation of 5 aliases.
In this manner, I can control which email is being spammed, example:
I create an account with a new entity; I create the specific alias:
-Mynametag.newentity@relay.firefox.com
If I start to receive junk mail from "newentity", then I delete the alias.
I have done that for many years, unfortunately, it means that I need to create a new email address each time I enroll, which means my computer currently reads tens of email addresses.
So you should give the option to the user to create his own alias, and remove the limit of 5.

Edit on July 31st, 2020:

To avoid collisions, or similar prefixes, you can always have a validation running at creation time; I also add a string to make my alias unique, such as the date at which I create it:
20200731NewEntity@p6.firefox.com
This has two benefits: I can organize my email aliases list in chronological order, increasing or decreasing, and I always keep track of the date at which I created the alias.

If a user has many Relay IDs and happens to get emails which for some reason are not easily identifiable from the content as to which account sent them, then it would be useful if the information in the forwarding header also included the information from the Account note field which was provided when the ID was created.

i currently have burner email extension which allows you to use 5 email addresses which can be used over and over again without logging in. i was expecting relay to be the same but it seems i have to log in to use it every time, and when i close the tab or firefox browser, i have to log in again.i'm guessing i'm missing something : ) or not ? but either way i'm sticking around to watch it grow , thanks its still useful though, just a bit different.

sorry for late response, after using a clean profile i'm guessing my problem was an addon clash as it works as expected now : ) gonna check them out by disabling one by one - thanks

so it is temporary containers addon that was causing it for me.

So far, so good.
Work as expected.
Easy setup.

Seems to work very well. 4 instead of 5 stars because only 5 aliases is not enough for my needs...but I guess this will maybe increase in the future.