How to Use Firefox Spellchecker (& Install 5 Better Ones)

Firefox has a built in spell checking tool, however it has limited functionality and only highlights spelling mistakes, but doesn’t offer: auto-correct, synonym proposals, 1 click spelling correction, rephrasing broken sentences or built-in dictionary.

If you’re fine with these limitations, and only care for the highlighting feature, then follow these steps to activate spell checking:

How Activate Firefox Spellcheck on desktop & laptop

1) Press the Menu button in the top right corner, and go to Settings.

2) Scroll down to the “Language” section and tick the “Check your spelling as you type” option.

Any spelling mistakes you make should now be highlighted like so:

Firefox spellcheck on mobile devices:

Unfortunately, Firefox has no built in spell checking feature, on it’s mobile browser. You must instead rely on the auto-correct features of your device’s keyboard.

If those don’t work as you’d like, then the next best option is to install spell checking apps.

Most of these replace your keyboard, but others function as word editors where you directly type in them and they spell check the words as you go.

Best Firefox spell checking add-ons

As mentioned previously, Firefox’s spell checking features are fairly limited. Fortunately, you have the option to install spell checking add-ons that are vastly better than the built in features in Firefox.

How to install a Firefox add-on

To install a spell checking add-on (or any kind of Firefox add-on for that matter), open the Menu button on the upper right side and navigate to “Add-ons and themes”.

This will take you to a menu where you can browse Extensions, Themes and Plugins.

In the search box you can then simply type in “spell checking” and you’ll get a long list of spell checking plugins.

Click the plugin you find interesting, and in the next screen press the “Add to Firefox” button.

Some add-ons (such as Grammarly) will ask you to create an account before you can use it, while others do not.

After installing, you’ll see the add-on in the top right corner. Clicking on it will open up various options for that particular add-on.

For most spell checking add-ons you don’t need to do anything, and they will work automatically in the background.

Grammarly Free

Grammarly is the most popular spell checking software, because it works surprisingly well, is easy to use and is available on all mobile devices and all major browsers (including Firefox).

Here are some things Grammarly Free can do:

  • Correct spelling mistakes.
  • Correct basic grammar errors.
  • Fix punctuation.

The vast majority of Grammarly users will be satisifed with the Free version, but the paid Premium plan offers a few nice perks:

  • Plagiarism detector.
  • Synonym proposals.
  • Sentence rewriting.

Grammarly Add-on for Firefox Desktop

Grammarly iOS | Grammarly Android


A close competitor to Grammarly, it too comes with a Free plan. Unfortunately however, the free plan will only correct the first 10,000 characters (around 1,500 words) in a text.

The advantages of LanguageTool are it’s slightly better suggestions and user interface, better privacy policy and the fact that it’s a free and open source software.

The free version will correct the following:

  • Basic grammar errors.
  • Spelling mistakes.
  • Fix punctuation.

The paid Premium plans upps the character limit to 100,000 per text (~15,000 words), Google Docs and Microsoft Word integrations, plus some extra stylistical tools.

LanguageTool Add-on for Firefox Desktop


Another free spellchecker with a Firefox integration. It’s results aren’t as good as Grammarly’s but it does come with an unlimited amount of characters, unlike LanguageTool.

Perhaps the biggest selling point of Linguix is its price,: $8 per month vs $12 for Grammarly.

It’s still not as affordable as LanguageTool however, which can cost as low as $4-5 per month, depending on what promotions you may find.

In terms of what it corrects, it offers the basics covered in other spellcheckers:

  • Basic grammar errors.
  • Spelling mistakes.
  • Punctuation improvements.

Linguix Add-on for Firefox Desktop


ProWritingAid is less a spellchecking app, and more a style guide to writing. It does offer spellchecking, but it’s most powerful features offer extensive style suggestions such as:

  • Passive voice detector.
  • Synonym suggestions.
  • Repetitive words.
  • Convoluted phrases.
  • etc.

On top of that, ProWritingAid offers the basic functions seen in previous spell checkers:

  • Basic grammar errors.
  • Spelling mistakes.
  • Punctuation improvements.

Finally, the biggest advantage of ProWritingAid is that the Free version has the exact same feature set as the Paid one.

The only difference is that the free version has a 500 word limit in place, but that should be enough for most light users.

ProWritingAid Add-on for Firefox Desktop spell checker

According to, they catch 60% more spelling and grammar errors compared to Grammarly.

It comes with a Free version, which also includes a Firefox add-on, as well as a monthly paid version at a price of $25 per month (which is rather steep).

Unfortunately, it has no mobile app, only browser add-ons. Add-on for Firefox Desktop

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