The Harper Firefox Extension

Harper is available for the millions who rely on Firefox for fast, private, and independent browsing. Unlike most grammar tools, Harper's Firefox extension performs all analysis locally—never sending your text to the cloud. Emails, chat messages, blog posts, and comments benefit from real-time grammar improvements, with your privacy intact.

To install, head to the Firefox Add-ons site and select 'Add to Firefox'.

Curious how it works? The Firefox extension runs entirely on harper.js, our open-source JavaScript library.

Updating the Extension

We're constantly improving our grammar engine and introducing new features to our Firefox Extension. To get the best experience with Harper, make sure your installation is up-to-date.

Your browser will automatically update the extension to the latest version as soon as it is available. If it is delayed, you can initiate a manual update yourself by following this guide.