Markdown is a lightweight markup language which uses plain text to describe formatting information, such as # Heading, 1. numbered list, **bold**, etc. This add-on identifies markdown documents by the extension in the URL (.md, .markdown, etc.). When you navigate to a markdown document, if the content is plain text, this add-on formats it into HTML (with headings, bold text, etc.) as described in the document and displays it directly in your browser. Features

Renders markdown files on the web and local files (file:// URLs).
Rendering is triggered through a button in the URL bar.<br /> Automatic rendering is available optionally (requires more permissions to check pages for markdown).
Works securely, by rendering pages inside a sandboxed iframe.
Adjustable rendering style:
- Out of the box dark mode support
- Pick page styling from default or github-lookalike.
- Pick code coloring from all highlight.js styles
- Add your own custom CSS (in the addon preferences)
Use a separate extension page to for heavy pages and environments that try to download markdown files, with
- Light browser footprint, by rendering pages in a separate worker thread
- One-time file picker confirmation, to access local files
Prepending ext+view-markdown: to an URL opens that page in the extension for rendering.
Supports header anchors (i.e. links).
Optional markdown syntax extensions:
- checkboxes,
- footnotes,
- fancy lists (e.g. roman numerals)
- laTeX,
- mermaid.js diagrams
- front matters,
- and emojis.
Download rendered result as static HTML page
Link to page source
Respects website security, including Content-Security-Policy headers, by not automatically injecting code into such pages even when automatic rendering is enabled. Rendering can be forced manually through the URL bar button.

⚠ On Linux and macOS, due to Firefox limitations, your browser may try to download a local markdown file instead of opening it. Simply prepend ext+view-markdown: to the file:// URL and confirm the access, or open the markdown viewer page through the toolbar button and select the desired file from a file picker. Permissions This add-on requires minimal permissions to do its job. There are:

Storage (mandatory, not shown by Firefox), to store preferences (including your personalized CSS) in your sync profile.
Active tab (mandatory, not shown by Firefox), to access a page’s URL and contents for rendering, when the URL bar button is clicked.
Host permissions (optional, presented as “access data on all websites”), to check pages whose URLs have markdown file extensions (.md, .markdown, etc.) for renderable markdown.