On Chrome instead? See our best Chrome extensions for Gmail roundup. On Safari on a Mac? See our best Safari extensions for Gmail roundup.
Firefox has a smaller add-on catalog than Chrome, so it is worth knowing which Gmail extensions are available and worth installing. Every extension below is live on Firefox Add-ons and adds something real to Gmail, from keyboard-driven speed to read receipts, dark mode and encryption. They are ordered by how much they change your day-to-day inbox.
On Chrome instead? See our best Chrome extensions for Gmail roundup.
Prefer the short version? Start with CMDK for Firefox, the productivity add-on covered first below.
1. CMDK: the productivity layer
CMDK turns Gmail into a keyboard-first inbox. You get a command bar (Cmd+K or Ctrl+K), 25+ shortcuts for reply, archive, delete, label and snooze, read receipts that show when your sent email is opened, natural language snooze and follow-up reminders, snippets, and a split inbox that separates work, personal and project mail into tabs. It sits on top of Gmail, so nothing about your account changes. CMDK arrived on Firefox in 2026 with the same features as the Chrome version.
Full disclosure: we make CMDK. We put it first because it is the extension that covers the most ground, and because it is the closest thing to Superhuman that runs inside Gmail on Firefox.
- Best for: speed, read receipts, snooze, and shortcuts in one extension
- Price: 15-day free trial, then from $5 a month
- Get it: CMDK on Firefox Add-ons
2. Checker Plus for Gmail
Checker Plus gives you desktop notifications for new mail and lets you read, reply, archive and delete without opening a Gmail tab. It handles multiple accounts and has a voice-notification option. If your main frustration is missing new mail while a Gmail tab is buried, this is the one to add.
- Best for: desktop notifications and managing mail without opening Gmail
- Price: free, with an optional donation
- Get it: Checker Plus for Gmail on Firefox Add-ons
3. Dark Reader
Gmail does not offer a true dark mode on the web. Dark Reader generates a proper dark theme for Gmail and every other site, with per-site controls for brightness, contrast and sepia. It is one of the most-installed Firefox extensions for a reason.
- Best for: a real dark mode for Gmail and the whole web
- Price: free and open source
- Get it: Dark Reader on Firefox Add-ons
4. LanguageTool
LanguageTool checks grammar, spelling and style as you type in Gmail compose, across dozens of languages. It is a strong open-source alternative to Grammarly, which is also available on Firefox if you prefer it.
- Best for: grammar and style checking inside compose
- Price: free, with a paid Premium tier
- Get it: LanguageTool on Firefox Add-ons
5. Mailvelope
Mailvelope adds end-to-end OpenPGP encryption to Gmail so you can send and receive encrypted email without leaving the browser. If you handle sensitive messages and want encryption that Gmail itself does not provide, this is the standard tool.
- Best for: end-to-end encrypted email in Gmail
- Price: free and open source
- Get it: Mailvelope on Firefox Add-ons
6. Todoist for Firefox
If you run your tasks in Todoist, this extension lets you turn an email into a task in a click, so follow-ups leave your inbox and land in your task list. It is a clean way to stop using your inbox as a to-do list.
- Best for: turning emails into tasks
- Price: free, with Todoist paid plans
- Get it: Todoist for Firefox on Firefox Add-ons
7. Webmail Ad Blocker
Gmail shows sponsored messages at the top of the Promotions and Social tabs. Webmail Ad Blocker hides those ad rows so your inbox only shows real mail. It is a small quality-of-life fix that adds up over time.
- Best for: removing sponsored rows from Gmail
- Price: free
- Get it: Webmail Ad Blocker on Firefox Add-ons
How to install a Firefox extension for Gmail
- Open the extension’s page on Firefox Add-ons.
- Click Add to Firefox and confirm the permissions.
- Open Gmail and reload the tab so the extension loads.
You can run several of these together. A common setup is CMDK for speed and read receipts, Dark Reader for the theme, and Checker Plus for notifications.
Frequently asked questions
What is the best Firefox extension for Gmail productivity?
CMDK is the most complete productivity extension for Gmail on Firefox. It adds a command bar, keyboard shortcuts, read receipts, snooze and a split inbox, all inside Gmail.
Are these Firefox extensions free?
Most are free. Dark Reader, Mailvelope and Webmail Ad Blocker are fully free. CMDK, LanguageTool and Todoist are free to start with paid plans for more features.
Do Gmail extensions work the same on Firefox as on Chrome?
For the extensions above, yes. CMDK in particular runs the same feature set on Firefox and Chrome, and one account works across both.
Can I get read receipts in Gmail on Firefox?
Yes. CMDK adds read receipts to Gmail on Firefox, showing when your sent email is opened.
Want the biggest upgrade first? Install CMDK and press Cmd+K.
