Spell check is highly inaccurate even allowing for differences in US & UK spelling.
Grammar check is a hoot.

Last and most critical application inserts promo codes that really dick up the results to the point I'm getting error messages for the extra codes.

The very first world it decided to spell check? [not grammar] was in English correct but in American wrong as they miss out letters all over the place. In this case changing the meaning or meaning one of two things. Making uncertainty where English had clarity. I have removed it. It lasted 3 minutes. I suspect my grammar is better than the usual user. I still know that then and than are different, quite different.

Okay if you're not good a grammar, but only really useful for Americans - can't be changed to English spelling.

complete waste of time, slow inefficient, induces errors of it's own making me take the time to correct them.

Do not use. At all.

Not suitable for fast typers, incredibly slow and has now started a war with Adblockers because of their YouTube adverts. I have uBlock origin installed and yet this still gets through. Complete BS.

Also requires you to sign up for an account, in which several adverts didn't tell you about, all for a crappy spellchecker plugin.

they just want to collect data (what you write on youtube and facebook , a complete scam

it block dictionaries and do not works at all as expected (easy expected)

It is so annoying. grammarly grammarly grammarly ... I already hate them. Watching one single interview being interrupter 5 (FIVE!) times by this irritating stuff

It's not even working... BS

Requires you to signup for an account. Doesn't mention that in the description.

NOT WORKING FOR THE Firefox 55.0b8 64-bit *version.

Serious bug, stopped working, keeps prompting me to login, I do, same message, useless in Fireforx

I submited the solution of fixing blank popup page issue via their support as a paid user long time ago, but their support refused to pass the message to devs...

I tried adding a forum post to MSDN. It appeared peppered with all the HTML source/tags from Grammarly attempting to fix my technical words that it didn't understand. Hence I had to copy/paste to notepad, remove them all, uninstall grammarly then paste the text back into the forum post.

It is helpful sometimes, but many times it is annoying. You cannot get a good answer or it is suggesting things incorrectly. There is no way to add to the dictionary if it "thinks" you are wrong. Any terminology outside of an 8th grade education level is not understood.

The biggest deal is on some form-fill-in sites using the later HTML5 code, parts of the form disappear. I just went back to the old spell checker.

I may check it out again in a couple of years. I would NOT pay for a subscription. The beta is not ready for charging any money. There is No Way I would pay. This add-on is very buggy.

Paid for the premium service and the apps included are all buggy and useless. Will not keep you logged in to your account even with Premium, does not work as it says it will across all web writing. Stick with the free version as the apps are overpriced and don't work properly! Also no app for mobile which is crazy for the prices they are asking for.

Again and I again the customer service told me to uninstall and re-install it.
It doesn't work.
If even it is already enabled Mozilla propose me to install it like it was not present yet.
I am premium client. Disappointing.

The drop-down is empty... i am a little bit disappointed. Hope the Tech group can fix this...

It is a great idea but it does not work for me unfortunately, it keeps telling me to log in even though I have logged in a thousand times and I cant get it to review anything I write.

It does not work. Please fix it.

Drop down box is blank. Doesn't run in my FF browser. Have to open the site to check my writing. Have to use Chrome to edit web pages on the fly.