Grammar checking tools fall into two categories: cloud-based (Grammarly, LanguageTool) and local. Cloud tools process your text on remote servers; local tools run entirely in the browser.
AI Writing Assistant for Firefox is a local grammar tool.
What it does
The extension adds grammar checking and text rewriting to Firefox. Highlight text on any page, right-click, and select the assistant. It identifies grammar issues and suggests rewrites — running entirely within the browser.
AI Writing Assistant — Firefox Add-ons
How local processing works
The grammar model runs inside Firefox using the browser’s JavaScript engine. When you submit text, it is processed locally — no network request is made to any external service. Your text does not leave your machine.
When local processing matters
For most casual writing (emails, social media, blog posts), cloud tools like Grammarly are accurate and convenient. Local processing is not necessary.
For sensitive content, local processing changes the privacy calculus:
- Legal writing: drafts that are attorney-client privileged
- Medical notes: patient information subject to HIPAA
- Financial content: non-public information
- Personal content: journal entries, private correspondence
Sending any of this text to a third-party grammar API creates exposure. A local extension eliminates that exposure.
Accuracy trade-offs
Cloud grammar tools (Grammarly, LanguageTool) run large models on powerful servers. Local models run in the browser and are necessarily smaller. For complex grammar edge cases, cloud tools will generally be more accurate.
For standard grammar checking — subject-verb agreement, punctuation, sentence structure — local processing handles most cases correctly.
Setup
- Install from Firefox Add-ons
- The extension activates automatically
- Highlight text on any page → right-click → select the writing assistant
No configuration, no account, no API key.
Install AI Writing Assistant for Firefox
AI Writing Assistant is one of 11 Firefox extensions I built — see the full series.