Landing page reports mail not sent when registering to mailing list on Firefox.

[ghost]

Describe the bug
When using both my ProtonMail and Gmail addressess to register to the mailing list, the landing page reports "Mail was not sent, please report the issue here"

To Reproduce
Steps to reproduce the behavior:

1. Go to 'https://codidact.org/'
2. Input a mail address on the 'Join our mailing list' prompt
3. Click 'Subscribe'
4. See error

Expected behavior
Subscription should succeed or print a more detailed reason for failure.

Desktop (please complete the following information):

• OS: Ubuntu Mate 18.04
• Browser: Firefox
• Version: 80.0.1 - canonical - 1.0

Additional context
Enabled Firefox extensions (all up to date):

• Privacy Badger
• HTTPS Everywhere
• uBlock Origin
• Skip Redirect
• Decentraleyes
• DuckDuckGo Privacy Essentials

Disabling the extensions doesn't fix the issue.

[galegosimpatico]

Duplicate of #51 or if you prefer the other way around.

[dagelf]

Still ongoing.

[Daksh14]

Cannot reproduce this on firefox 93.0 (64-bit), need more info and reproducing systems to proceed

[galegosimpatico]

Cannot reproduce this on firefox 93.0 (64-bit), need more info and reproducing systems to proceed

I'm not around, but #59 (comment) (likely duplicate, is fixed).