Unread Badge for Gmail™ by Yaakov Avihai Shai

Unread Badge for Gmail™ puts your unread mail count directly on the Firefox toolbar. No popup, no dashboard, no sign-in flow - just a number that updates in the background, and a click that opens Gmail.

How it works
The extension reads Gmail's own unread-count feed using the Gmail session you're already signed into. There is no OAuth flow, no API key, and no account setup. If you're signed into Gmail in Firefox, it works.

Multiple accounts
If you're signed into several Gmail accounts, the badge reflects the total across them.

What it does not do
No analytics. No telemetry. No tracking pixels. No third-party servers. The extension talks to Google and to nothing else. Message content is parsed only to count unread items and is discarded immediately- nothing is stored and nothing is transmitted anywhere beyond the request to Google that your browser was already authorized to make.

Permissions
The extension requests only the access needed to fetch the unread feed and update the toolbar badge.