The best spelling & grammar checker for Firefox
Looking for a smarter way to spot and fix mistakes and typos? Want to write faster and better on Firefox? Other extensions not cutting it? Forget your old writing tools. The writing revolution for Firefox is here.
Add to Firefox 
Add to Chrome 
Add to Edge Spelling & grammar checking
MerciApp delivers the best spelling and grammar checker on the market. No exaggeration!
Style enhancement
Turn to clunky, long-winded sentences into clear, flowing prose with our style enhancement features.
Smart rewriting
Thanks to our AI-powered updates, MerciApp now provides contextual rewrites. A must-have for all writers.
Deep dive
Why choose MerciApp?
MerciApp brings precision and polish to your writing on Firefox. Say goodbye to mistakes and hello to effortless, professional writing. With the MerciApp browser extension, every word matters and every sentence shines.
A writing powerhouse
Three decades of linguistic expertise at your service! MerciApp has already won over 200,000 writing enthusiasts. Are you next?
Think you’re safe from embarrassing spelling, grammar, or syntax mistakes? Think again. The future of writing is here. Are you ready?
Unmatched ease of use
In just two clicks, the MerciApp browser extension transforms your Firefox browser into your very own language assistant. No hassle, no complicated set-up.
Ready to make every single sentence sparkle? The future of writing is at your fingertips.
For words that shine online
Make spelling, grammar and style mistakes a thing of the past. MerciApp has your back wherever you work- Gmail, Google Docs, LinkedIn ou Facebook…
One single browser extension. Flawless writing, everywhere, every time.
Try MerciApp for free
Take MerciApp for a spin for free! Love it? Go premium for even more features. Just exploring? Keep leveling up your writing online without spending a dime.
Ready to take your writing to the next level?
Set up MerciApp for Firefox in 3 easy steps:
Download the browser extension
Fast, easy and free. No credit card required.
Create your MerciApp account
Almost done! Set up your account in a couple of clicks to unlock the spelling and grammar correction.
Start correcting
MerciApp scans your text to spot mistakes and suggest improvements. You pick what works for you! Just choose the corrections you want to apply to improve your text.
The must-have spell checker for Firefox
Looking for a smart, fast and precise spelling and grammar checker for Mozilla Firefox? Forget other extensions. It’s time to elevate your writing with MerciApp. Trusted by experts. Used by thousands.
In a matter of clicks, transform your Firefox browser (or Google Chrome or Microsoft Edge) into a super-accurate writing assistant. Our extension scans through your texts, spotting mistakes and anomalies with unmatched precision.
Gmail, LinkedIn or Facebook… wherever you’re writing, make it impeccable with MerciApp. Try MerciApp for Free. So much more than another boring spell checker, this is a correction game-changer. Installing it? It’s up and running in seconds.
And as for privacy, your data is kept securely in our servers. Still not decided? Try our spelling and grammar checker for free for 30 days. On a quest for flawless writing? Welcome to the magical world of MerciApp.
Not on Firefox? No problem, we also have extensions for Chrome and Edge.
We read (and love) your feedback
You say it best
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J’aime la facilité avec laquelle les corrections se font et le temps que ça fait gagner à l’équipe. J’aime recevoir un e-mail sans faute d’orthographe.
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Très facile à utiliser, j’aime aussi les explications de MerciApp qui me font progresser au quotidien.
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Quand on échange avec des décideurs de haut niveau, une faute dans un e-mail de prospection peut décrédibiliser la société. Chaque e-mail important était relu par une autre personne. Au final, je me suis rendu compte que Gmail laissait passer beaucoup de fautes de grammaire. Merci MerciApp !
We launched MerciApp in 2020 with Diagonal, a French leader in proofreading.
With one simple goal: help 300 million French speakers worldwide communicate better.
Arthur Ollier
Co-Fondateur et CEO de MerciApp