Open Firefox and visit the Firefox Add-ons page to install the Grammarly browser extension. Click Add to Firefox to start the download. Click this link to open Mac App Store and install the Grammarly browser extension. Click Get > Install to start the download.
How do I add extensions to Firefox browser?
Click the “Extensions” tab to browse, or use the search box at the top of the screen. Once you find an extension that you like, select it to see more information about it. Click “Add to Firefox” to install the extension. A pop-up will appear with information about the permissions required for the extension.