Jira Assistant add-on not found in firefox marketplace

From README.md I understand JiraAssistant is also supported for Firefox. However, the link to the mozilla add-ons marketplace (https://addons.mozilla.org/en-US/firefox/addon/jira-assistant/) takes you to an error page.

Is the firefox version still supported? I could not find any information stating the opposite (just two similar issues where it seems the problem was fixed)