Many features only in Pro version.

I tried it and uninstalled. It did not catch an uncapitalized first word in a sentence.

For new users make sure you "auto saved" all your documents every minute as it freezes and crash your web pages very often. When crashed a yellow bar appeared that reads "a script "Grammarly for Firefox" is slowing down your browser, temporary disable or stop it." If you are lucky only one tab crash, if not all and never respond again. Got to turn off power to restart your computer (very annoying).

Grammarly was completing my sentences with words that were not mine. I could not get rid of it. To my mind it is a defect in the program. There is no phone number or address to ask for help.

It offers very good functionality, however almost no configuration options. The plugin runs by default on all pages resulting in huge performance impact, severely increased memory use for Firefox and indeed privacy concerns.
Have you just started to type something sensitive on a page without remembering to disable Grammarly first? Bad luck, your data is already on their servers.
Setting the plugin to be disabled by default and only enabled on demand would be absolutely necessary. The way it is now, is shady and too pushy.
I can see how they want it to run everywhere, but still, this is a big no-no, to by default automatically send all my typing to a remote server.
Also the resource usage is really bad. If you use few tabs and restart browser every offten, probably it's fine, but I usually have several tens of tabs in variety of windows and Firefox running in one go for a week. Now, if you are such a user, disable this, and you'll be amazed how much better the overall responsiveness of Firefox will become.
Long story short: it offers nice feature, but the cost cannot be justified.
I'd just go to https://app.grammarly.com/ if I need writing assistance, and keep away from this plugin for good.

some time grammerly just sits there... dose nothing... just like right now as i am filling out this review...

Grammarly does not allow me to make any notations in Google Contats.

CREATE AN ACCOUNT TO
See detailed corrections.

In fact, that's mean without login you basically could not see any correction except for capital letter correction or something else like this.

I liked it at first (a year ago). It doesn't work now and nothing I do will fix that.

i, like other users find it doesn't work, for me at all, with Firefox 62.0.3

Works intermittently on Firefox Quantum 62.0.3 (64-bit), therefore I question the point of paying for a premium service.

Love it when it works. It seems that it is so schizo on FaceBook and it is suppose to work on this page and it does not. I contacted their customer service and got nowhere quick with them. Either the customer service people are not kept aware as to what is going on or just simply stonewalling. I give up with Grammarly.

Fine when not logging itself off, which happens frequently- just found and placed the tool bar button which- hopefully- logs me on in a whif'...

It slows down the pc with Premium subs.

I agree with the reviwer who said: In Google Contacts, when Grammerly is active, I can not see my NOTES field because Grammerly conceals it with its badge. It's very irratating to have to click on the grammerly badge to see the note field, which disappears again when I return to the contact view.