Markdown Viewer Webext by Cimbali

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.