I find this service useful and the plugin nice. However, I experienced an issue and I found no place where to report it.
The issue: the plugin create a wrapper around the email field (class fx-relay-email-input-wrapper) with z-index of 99999999999999.
The label of that field was supposed to be over the field (z-index 100), but is actually hidden by the field itself (that normally has a z-index of 10) and this breaks the layout.
Thank you to consider this scenario in your tests.

The idea of a relay junkmail with option to enable/disable redirection is excellent!

However, I find the addon and the user experience to be near useless.

BEST UX practice:
1. Click on email field, addon suggests to input relay address.
2. Click on any alias, it gets submitted to field. Nice and easy.

Current flow:
1. Click email field, addons says "You have X aliases left", only "Manage" button available;
2. Click Manage, get redirected to Mozilla sign in page;
3. Sign in to Mozilla;
4. Manually copy alias from the list;
5. Go back to page with email field;
6. Manually paste the alias.

便利なんですが、転送されてきたメールで相手のメールアドレスがわからないのはどうしたものか...
また、エイリアスの管理画面で作成したエイリアスにメモなどを書き込めるとさらによいと思いました。今後エイリアス数上限が上がること期待してしまいます。
It's convenient. However, you can't know to know the email address of the person to whom the forwarded email is coming from. That's a complaint.
And I thought it would be even better if I could write memos and so on to the alias I created in the alias management screen. I hope the maximum number of aliases will be increased in the future.

No tiene una función para enviar información sobre errores del programa, ya que como es una fase beta seria lo recomendable para que llegasen lo mas rápido posible, ya que no tiene esa función diré por aquí, que tiene un error, que al recibir los correos en la bandeja de entrada, no se muestran los caracteres especiales.

I can not understand why I need to install addon to use Firefox Relay. It can be server-side solution, no need to install addons essentially. No explanation/justification was displayed when I registered myself to Firefox Relay. I felt like I am forced to install unnecessary addons. I trust Mozilla and I believe this addon does not collectt our user data. That is why I installed this addon. I will not if other service provider requests me to same thing.

Please add the ability to enter existing relays into text boxes opposed to opening extension in order to copy an alias.
Otherwise no issues yet !

Firefox Relay Service and Unicode escape sequence.

That's what I get:
\u0417\u0434\u0440\u0430\u0432\u0441\u0442\u0432\u0443\u0439\u0442\u0435
It's "Hello" in Cyrillic.

--UPD--

It was "Body" of email. Google Mail.
Also, answer notification came to me directly to my main mail (not relay) and contains this:
We & #39 ;re
and
& quot; From & quot;, & quot;Subject & quot;, or & quot;Body & quot; of the email?

Idk is that google, mozilla or both.

По этой ссылке скриншот того, как пришло письмо после прогона через Релэй , не спам и не вирусы https://prnt.sc/u3hpb7

A small downside to this addon, it should be possible from an email field to choose the temporary address already saved in the browser.

But I see that you can only create new addresses via the icon in the field.

if I want to take back a temporary email address already registered, I have to go in the address management to make a copy/paste.

FR: petit bémol a cette addon, il devrait-être possible a partir d'un champ email de choisir les adresse temporaire déja enregistrée dans le navigateur.

Or je constate que l'on ne peut que créer des nouvelles adresse via l'icone présente dans le champ.

si je souhaite reprendre une adresse email temporaire déja inscrite, il faut que j'aille dans la gestion des adresses pour faire un copié/collé.

I love the idea! Unfortunately the site I was trying to use it on (mjam.net) didn't seem to think that the *@relay.firefox.com address was an actual email address and prompted me to enter one over and over again.

So for now I cannot give it a better rating, but I will gladly change it if I was somehow mistaken, the issue is not with firefox relay, or the issue is fixed.

EDIT: keep up the good work!

Great idea. Unfortunately, the beta refuses to safe preferences (specifically the setting to stop replacing all email fields on websites). This makes it difficult-to-impossible to log in to some sites.

Good work. Would you add an option to copy email address in one click?

This is exactly the type of of app/extension I've been looking for for ages. Mozilla creates yet another legitimate, simple way for users to bolster their online privacy.

Love the idea here, but have a problem with encoded emails.
I receive emails in Hebrew, but the relayed emails appear Jibrish. I assume the relay does not work will for encoded languages.

Estensione quasi inutile... Problemi più gravi:
- Manca la possibilità di visualizzare le email bloccate
- Manca la possibilità di poter scrivere delle note vicino agli indirizzi (es. il sito dove è stato usato etc.)
- Non si può cambiare l'indirizzo email a cui vengono inviate le email

Absolutely love this idea and the execution is great too. I would absolutely pay to be able to generate a new, unique email address for every new site, rather than be limited to just the 5.

Excellent outils, je n'ai subi aucun bug sur cette béta. Bravo à toute l'équipe !!!

I wanted to try to register to 9gag.com using relay and the address is blocked.
I really didn't want to write a review yet as I couldn't play with it enough, but this is the only way to contact you.