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Preview of Markdown Viewer (MyProjects)

Markdown Viewer (MyProjects) by Alffy

Render local Markdown files in Firefox as styled pages: GitHub-Flavored Markdown, code highlighting, KaTeX math and live Mermaid diagrams, in dark or light. Fully offline: your files never leave your machine, and no data is collected.

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The showcase header: the MyProjects Markdown Viewer Feature Showcase, with its offline-only badges (renderer, MyProjects dark theme, local `.md` scope, and "data collection: none"), a table of contents covering all eight sections, and the opening text-formatting section.Deeply nested and mixed lists render correctly — ordered sub-lists, unordered lists, and the dark theme together — alongside a heading anchor and KaTeX math.Task lists with real checkboxes, plus a rich aligned capability matrix — GFM tables, heading anchors, fenced code, math, and more, each with a clear mode and support note.Offline-safe ASCII diagrams: the extension's data flow, layered pipeline, and decision flow, drawn as monospaced art — no network and no library required.Live Mermaid diagrams in a sandboxed page: they render locally with securitylevel: strict and are re-sanitized, so no script can run through a diagram.A spread of Mermaid diagram types — flowchart, sequence, class, state, and pie — drawn as crisp live SVG, fully offline, with each SVG re-sanitized on top of a strict sandbox for defense in depth.The showcase from the top: a self-contained tour in the light MyProjects theme, with a clickable table of contents and rich inline formatting (bold, italic, strikethrough, inline code). Everything renders locally and offline.Headings and math, rendered cleanly. Every heading (H1 through H6) gets a clickable anchor so you can deep-link to any section, and KaTeX renders inline and display LaTeX entirely offline — sanitized before it reaches the page.
About this extension
Open local Markdown files in Firefox and read them properly — no upload, no account, no network.

Renders .md, .markdown, .mdown, .mkd and .mkdn files from file:// as styled HTML.
GitHub-style tables, task lists, strikethrough and code blocks with syntax highlighting (highlight.js).
Math with KaTeX, and live diagrams with Mermaid.
Dark and light themes; your choice is remembered.
Content sanitized with marked + DOMPurify.
Fully offline: no network requests, no telemetry, no data collected. Your files stay on your machine.
Open it from the toolbar (Ctrl+Shift+M), the right-click menu, or the sidebar (Ctrl+Shift+Y). A 24-hour render cache keeps large documents fast.


One-time setup: Firefox blocks extensions from local files until you allow it. On first install a short setup page shows the single toggle to enable — "Access local files on your computer" in about:addons. If you skip it, the toolbar icon shows a "!" badge and the popup explains the fix.

Requires Firefox 154 or newer.
Developer comments
v1.2.7 (current) — Fixes a page that had rendered correctly and was then replaced, a few seconds later, by the viewer's own "Markdown not rendered" message. Firefox runs the content script twice on one page; the second run found no Markdown left to read, because the render had already consumed it, and repainted the page with a banner. A page this viewer has already rendered is now left alone. No permission change; the render cache version moves to md-viewer-v1.9, so a page cached by an earlier version is rebuilt once after the update.

Renders local .md / .markdown files (via file://) with marked + DOMPurify sanitization. Fully offline and private — no data is collected, stored, or transmitted (data_collection_permissions: none). Supports clickable heading anchors, GFM tables, task lists, nested/mixed lists, fenced code blocks with syntax highlighting, blockquotes, strikethrough, KaTeX inline + display math, and live Mermaid diagrams (sandboxed, SVG re-sanitized). A persisted dark / light / auto theme. Edits re-render automatically on reload. Requires Firefox 154+.

v1.2.6 — Fixes a rendering collapse and an inline-math defect, and removes the two silent paths behind them. A Markdown file whose first lines are an HTML comment is served by Firefox as text/html; it used to render as one collapsed run of text and now renders normally (1880 paragraphs and 13 headings on the 748 KB file it was reported on). A single dollar sign no longer opens an inline formula, so currency and ordinary prose are no longer swallowed, while a real formula still renders. Any Markdown page the viewer cannot render now reports through a visible banner instead of leaving the browser's own rendering in place, and a degraded first render can no longer be cached in place of the better one (CACHE_VERSION md-viewer-v1.8). No permission change.

v1.2.5 — Declares two fewer permissions, neither used by this tree: activeTab has no call site, and contextMenus is a duplicate alias of menus, which is the namespace the code actually calls. The declared set is now storage, scripting, tabs, menus and unlimitedStorage; nothing was added. Also fixes GitHub-Flavored Markdown strikethrough parity — a single tilde in ordinary prose is now rendered literally, while a doubled pair still strikes through. Also fixes the options-page cache-version footer.

v1.2.4 — Adds a first-run setup page that opens once on install and walks the user through enabling "Access local files on your computer", with a live check that confirms the grant. Fixes the silent failure when file:// access is off: the toolbar icon now shows a "!" badge and the popup displays the exact steps plus a button that opens about:addons. Also fixes a cold-start "Rendering..." hang, a duplicate context-menu error after reload/update, and KaTeX fonts not loading on file:// pages. No new permissions.
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Permissions and data

Required permissions:

  • Access browser tabs

Optional permissions:

    Data collection:

    • The developer says this extension doesn't require data collection.
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    Add-on Links
    Version
    1.2.7
    Size
    2.03 MB
    Last updated
    5 days ago (Sep 21, 2026)
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