This has been working fine for a while, but I had to refresh Firefox for other reasons.
Then it is necessary to re-install the add-ons.
After installing Grammarly, Firefox could not get to any web page I requested.
After disabling Grammarly, Firefox would work without a problem.
Firefox does have a spell checker so I will stick with that to minimize having too many add-ons.

Running Firefox Quantum 61.0.1 (64-bit).

When I log into my PC as a different user they both play well together. Go figure?

Awesome

It is good, but buggy as hell. The administration refuses to work on these bugs. This extension is very buggy on Twitter if it works at all (up to what browser). If it is buggy on one service, I don't trust it to work on others.

Have to frequently reinstall. Sometimes a Blank screen sometimes refuse to make correction even it recommends . Just not very reliable same or similar issues with extensions for Chrome and Safari as well.

Very buggy with latest versions of Firefox. Read the console log as it is beating its brains out to contact an external server that is not responding.

Slows my computer down terribly. I had to turn it off until they fix it.

Also, since it is free, I have concerns that everything I type goes to their server where my data is extracted and sold.

i love how it USED TO WORK. But now it's a piece of crap. I make corrections and they don't not stick. The errors come right back.

The red line supposedly underneath words is somewhere else entirely on the page.

Absolute total buggy garbage and unusable.

Doesn't work with Firefox. What gives?

Poor integration with MyBB fourms.

This add-on doesn't work properly on the latest Firefox.

the add on is very useful but has a very poor integration in FF.

All suggestions are offset from the text making it almost useless in Firefox. The Chrome extension does not have this problem. I love it for Chrome... super helpful. This review is not an indictment of Grammarly, but of their extension for Firefox.

Useful functionality, but introduced lag when typing on some pages (i.e. gmail).

It's a good tool, but I had to uninstall it because it slows down the browser.

The warning lines and suggested corrections do not line up with the actual text.

I'm re-installing Grammarly to my Firefox browser and I hope that will solve my issues, but so far Grammarly and Firefox are not getting along and Firefox hangs up or freezes and I get an error message which says it's because of Grammarly. Extremely frustrating and a huge time suck. If this works, I will change my review. If not, I'm uninstalling Grammarly from the browser for good.

lose sending button on some websides

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.