Gmail Mono is a email extension for chrome. it's a free extension , it has 6 active users since released its first version, it earns an average rating of 0.00 from 0 rated user, last update is 1237 days ago.
This is based on https://github.com/ls42/gmail-mono and updated styles.css to force apply monospace to editable and subject.
You could download the latest version crx file or older version files and install it.
English.
You could find more help information from gmail mono support page.
You could send emails to publisher, or check publisher's website.
You could click to report abuse of gmail mono.