SquiggleSage by spanijel

SquiggleSage provides local writing help while you type in ordinary text inputs, textareas, and contenteditable editors on desktop Firefox. Firefox supplies native spelling underlines and dictionary corrections. SquiggleSage adds built-in English grammar, capitalization, typography, and style checks, with prominent red squiggles, clickable suggestions, and one-click replacement.

A draggable issue-count badge appears for the active editor. You can ignore a suggestion once, disable individual rules, choose checking categories and typing delay, or disable checking globally or for exact hostnames.

All processing stays inside Firefox. The add-on has no account, paid service, advertising, analytics, telemetry, remote code, cloud or AI service, third-party library, or network request. It does not transmit or persist editor text, page content, full URLs, or suggestions. It stores only local settings and exact hostnames that the user chooses to disable.

Automatic checking runs on HTTP, HTTPS, and local-file pages, including embedded frames. Within each page or frame, only the most recently focused or activated supported editor is processed.

Current limitations: the bundled writing rules are English-only; spelling uses dictionaries installed in Firefox; Google Docs, Google Slides, canvas-based editors, closed shadow roots, and some site-specific rich editors are not supported.

SquiggleSage is an independent project and is not affiliated with or endorsed by Mozilla. Firefox is a trademark of the Mozilla Foundation in the U.S. and other countries.