Present a Mozilla Account upsell button when users sign up for a newsletter

[drubino-mozilla]

When users sign up for the Firefox newsletter at https://www.mozilla.org/en-US/newsletter/firefox/ we present a "Thanks!" message. This proposal is to adjust this message to briefly explain the benefit of a Mozilla Account and offer a button to sign up. The adjusted copy and button would only appear if the user was actually in Firefox Desktop (not mobile) and was not already signed-in. The signed-in state should be available from UITour. The button would navigate to accounts.firefox.com in a new tab, using a URL that 1) pre-populates the email the user gave for the newsletter, and 2) signs the user in to the browser at the completion of the flow.

Note that this is just a button to start the Mozilla Account flow. It does NOT propose to sign up a user for a newsletter and an account at the same time, or do anything that requires an update to the privacy notice.

This work can also be applied to other newsletter entry points, if doing so is not expensive:

https://www.mozilla.org/en-US/newsletter/
https://www.mozilla.org/en-US/newsletter/family/
https://www.mozilla.org/en-US/newsletter/security-and-privacy/
https://www.mozilla.org/en-US/newsletter/mozilla/
https://www.mozilla.org/en-US/newsletter/developer/

[drubino-mozilla]

This is the current "Thanks!" message that displays after email is provided. This is what we would adjust and add a button to.