There is clearly a significant memory leak issue on Firefox. As a paid subscriber, I am no longer able to use it. Firefox freezes and becomes unusable.

I am a premium user, and unfortunately the Firefox extension is causing serious issues. It consumes up to 32 GB of RAM, which makes my computer freeze and eventually restart on its own. This is not an isolated case — it happens on two different computers, so it’s clearly not a hardware issue on my side.

This makes the extension completely unusable despite paying for the premium service. I would expect much better stability and performance from a paid product. Please investigate and fix this as soon as possible.

It used to be a 5 stars plugin, but since the January 2026 update, whenever I switch this plugin on, firefox crashes on my Macbook. It totally eats all the memory. I reported it as a bug more than a month ago but haven't heard from them. So, for now, it will stay switched off.

It's even worse than the built in spell checking of FF.

It isn't shown on here, but if you click the link in their "about" section, you can see that they now use AI to scan and check your text, which is probably why I've been getting so many errors in it lately, including ones for proper nouns that weren't there before.

In short, don't use it. It doesn't work like it used it, and as it is using AI, there is the potential for it to be using your own text to train models. Uninstall it if you have it already.

Causes a memory leak.

This is an evil extension!!! Why? We have been scratching our heads to find out why there is a consistent memory leak issue. It has wasted a lot of our precious time! Moreover, we even consider adding more memory but the memory price is very high now! We have never felt such pain in recent years! We are very angry that this poor plugin is so popular and has not fixed this issue in the shortest time.

A huge thank you to the person who wrote a review below. I've been using this extension for five years, and in the latest version, either there's an unintentional bug, or the developers intentionally introduced a leak that hadn't existed for 10 years.
This extension is currently causing a memory leak in the browser, even when I'm not opening anything and only on one page. It reaches 60 gigabytes for me, after which everything in the OS starts crashing with errors, from the browser to other programs.

I've been racking my brains for 2-3 weeks of torment, I couldn't figure out what was going on, because I've been using all the extensions for years and everything has been working without a hitch for a long time.
And it turns out that's what it is. The extension, which had been reliable for years, is now leaky and buggy, leaking 40-60 gigs of memory.
As soon as I removed this extension, everything has been fine for several weeks now.

I've been using LanguageTool for almost three years, and until recently I would have happily given it 5 stars.

Unfortunately, the recent changes to the free version have made the extension almost unusable for me. After the initial Premium trial ends, the extension no longer functions as a grammar checker, which completely defeats the reason I installed it in the first place.

I'm not giving 1 star because the software itself is bad. Quite the opposite — that's exactly why these changes are so disappointing. LanguageTool used to be an excellent free writing assistant, but now I'll have to look for an alternative.

I understand that developers need to make money, but the free version has become so limited that, for me, it has lost the value that made it worth installing.

It's been getting things more wrong than right now, words that are one letter off are suggested to be completely different words or even correct words are marked as misspelled.

Sold to a US company

It was a great tool but from about 2 weeks it completely slow down my Firefox :-(

Had to remove it after about ten minutes. Even with all the "fussy" options turned off, it's just far too annoying and constantly making idiotic suggestions which if followed, would often leave meaningless sentences behind. It might be handy for people who are terrible at writing and grammar. But it was way OTT for me. I just wanted something that would underline spelling mistakes in what I was writng, to help me spot typos when proof-reading.

So maybe I'm noy the target audience.

I was also not happy with the thought of everything I write on the web being sent off to be checked. Even if [as is always the case] the developers claim everything is very secure and encrypted... yadda yadda.

Neither did I like the fact that a lot of the functionality has to be paid for. Not something that was mantioned anywhere in the blurb, as far as I could see.

This WAS! The best spell checker for the web BUT NOW it is going behind a pay wall sorry but I can NO longer recommend this tool to use

I bought the premium bull..... and since then it went all down the drain.... After 30 minutes of work it slows down the browser like I would work on my toaster but I really have a high high end PC for Gaming and Development

I understand that the company needs to make money from its work, however wanting 20 € per MONTH for a grammar checker is insane to me. Harper is also open source and free, I switched to that. 20 € per year would be cool, but 240 € is a hard pass. :(

in 14 days the extension will be premium only and they except you to pay 20 USD a month for this extension


"how many times do we need to teach you this lesson old man?"

Absolutely no warning. They disable and remove the extension saying you must pay for it now. I go to check the pricing...$20.00 a MONTH!!!!! Are you insane. Grammarly is hundreds of times better and it's only $12.99 a month. Can you say the word bankruptcy! The employees of LanguageTool...time to go looking for a new job! Oh...and get this. The announcement says you must pay for it now. You click on it and it says it's $24.99 a month. You go directly to the site and it's $19.99 a month. They are charging an addition $5.00 to the people that have used their product for years. They did EVERYTHING wrong. No coupons on saying thanks for using our product. A discount for saying, hey, we get this comes as a surprise. This should help for a few months. Instead, they charge the users MORE!!!!

Opened download file and it was some map quest app or something.

Does not save or sync with the dictionary. The AI they have to help is a moron.

Prioritizing greed over It's long time users, or this just your bait‑and‑switch, Either way you've lost me and you should also be removed from Firefox recommended list.

Originally my rating was 5/5 stars; as of 08/06/26 I've now revised that to 1/5 Stars.

LanguageTool has genuinely been one of the most useful extensions and tools I've used in the past year or two. Sadly, the team has decided to lock the ENTIRE extension behind a paywall (with no "lite" or "freemium") version, I seriously can't even get the extension to pop up?? It's just not worth the price right now, but also I couldn't even pay them if I wanted to???

I wish they'd have taken a page out of the DeepL team's book and made it so LanguageTool was an available option for the Firefox Browser Sidebar. I can kind of understand locking the original functionality down, but now I have to have a whole separate tab open to their main desktop website if I want to use/check any part of it??? this whole update and functionality change is just... odd.

For the record: YES; I would actually consider paying for LanguageTool if the extension had more integration on Firefox and other platforms I'd love to use it on, like iOS*!

I do hope it see it improve at some point. The slow decline of LanguageTool makes me sad. I hope I can come back and edit this review to be more positive in the future. For now, I'll be looking for an alternative extension and recommend others do the same.


(*which I have my own gripes about.... mainly that giving LanguageTool my "full keyboard access" removes their non-Apple keyboard functionality of it Entirely for some reason? why does giving them Keyboard Access remove THE ENTIRE LANGUAGETOOL KEYBOARD? why does it get replaced with some shoddy, clunky, and laggy window that takes forever to spellcheck anything? This lack of truly integrated or easily accessible functions seems to be a pattern with LanguageTool right now and it does NOT help the "mandatory payment for our whole app/extension now" sting... sorry to sound harsh to a product i used to love but wow. it's disappointing)