Aside from the fact that it does not work on this web page, It is far from bulletproof and could conceivably cause problems for people learning the language. It is likely to cause people to click on selections without understanding the reason, which means that many people will learn nothing from using it, and become zombies. For example, it says that "in Facebook" is incorrect, and that I should use "on Facebook"., but when I use "in a browser" Grammarly does not tell me to use "on a browser". The reason it gives is that "It appears that the preposition in may be incorrect or unnecessary in this context. Consider changing or removing it." However, Grammarly says "preposition" should be "proposition" (incorrect) so you need to be careful when using this app.

Grammarly is injecting some sort of weird metadata into posts on some forums. In particular, the last one was on TechNet. Here is the link to the post in question. https://social.technet.microsoft.com/Forums/windows/en-US/cdfe7d70-2ff7-4025-87db-e26d452d27a2/how-can-i-completely-disableremove-readyboost-in-windows-81?forum=w8itprogeneral
It is very annoying, I am going to have to disable Grammarly for the time being which pisses me off because it's awesome.

This extension often hides the headings above the text boxes. I am clueless about what to fill in the text box. Please fix this bug ASAP!

Destroys textareas, super buggy in newest Firefox

Worked fine for several days, then stopped working. When it did, it also broke Win 10 spell check. I disabled Gammarly and can't get spell check back.

The Grammarly addon is broken for WordPress.com online editor. I have a really bad experience on Grammarly ever since I shifted to Quantum from Chrome. On Chrome it worked just fine, but here it needs more work. Hope the developers patch this.

You need to make an account to use it, and the extension also tracks you, placing ads on web pages that it never tells you about. Still, the actual spell checker is good.

When you select English UK. American words like Color and favor and organize. are not detected as error.

Not that great. I was writing a paper for a theatre class, and it told me that I needed to change all instances of "theatre" for "theater." It doesn't really help any more than any built in grammar device anyways, at least the free version doesn't.

Always need to login after every time opening of Firefox. Sometime shows error free, sometimes shows error for some same sentence. After selecting their suggested correction, it pastes the whole sentences again. So disturbing. I can't found any problem in the Chrome edition though.