This add-on would be useful for many people but on Firefox it just isn't usable. With Grammarly activated Firefox CPU usages goes through the roof on my Macbook. My Windows PC is bareable because it's a powerful machine, but on a slower work provided PC Grammarly is just too slow. I suspect Firefox's API just isn't providing the needed functions for Grammarly to work smoothly, but unfortunately this goes against the extension itself.