copy-latex-firefox-extension

CopyLaTeX

A Firefox extension that lets you quickly copy LaTeX code (KaTeX or MathJax) from equations displayed on websites like ChatGPT, DeepSeek, or any blog using mathematical equations. It works simply by hovering over an equation and clicking to copy the LaTeX expression.

Version 1.1: Now it also works with with Wikipedia and Wikiwand images.

Version 1.2: Now it also works for MathJax v3 (when there is no LaTeX code in the HTML) via API.

Version 1.3: Dark mode enabled and replaced check emoji with SVG icon.

Version 1.4: New feature! Select text (that includes formulas), right click on it and a Copy as Markdown (with LaTeX) option will appear.

Version 1.5: Now with Typst support!!!

Example GIFs

KaTeX

Demo-KaTeX

MathJax

Demo-MathJax

Wikipedia images

Demo-MathJax

Copy as Markdown

Demo-Markdown

You can use https://markdown-preview-katex.vercel.app/ to test this feature.

Copy as Typst

Demo-Typst

You can use https://typst-online.vercel.app/ to test this feature.

Generally any math, physics, or engineering-related blog or website. Some typical examples:

Host permissions and speed

You can check the javascript source code yourself. It loads after everything and is very fast and small sized. However if you want you can always customize in which hosts (websites) the extension loads or not:

Manage-extension-permissions

This is done in “Firefox Settings > Extensions & Themes” (or simply search about:addons), clicking the extension and choosing the tab “Permissions and Data”.

In case you turn off the “all sites” toggle option, you can also add manual sites that are not in the default list.

Manage-extension-permissions

And now the custom site should appear as a new toggle in the “Permissions and data” tab.

How it works technically

  1. Content Script (content.js):
    • For KaTeX
      • Automatically detects all <span class="katex"> elements on the page.
      • Extracts the LaTeX code from <annotation encoding="application/x-tex">.
    • For Gemini KaTeX
      • Extracts LaTeX inside data-math attribute.
    • For MathJax
      • Extracts LaTeX inside <script type="math/tex"> elements.
    • For MathJax v3/v4
      • Injects page script (mathjax-api.js) to extract LaTeX from mjx-container elements via MathJax’s API. Only possible via API and inject script because no LaTeX code present in the generated HTML.
    • For Wikipedia
      • Extracts LaTeX from alt attributes of images.
    • For all of them
    • Shows an overlay when hovering over the equation.
    • Allows clicking to copy the code to clipboard using navigator.clipboard.writeText().
    • Uses an inline <svg> to avoid external file dependencies.
  2. CSS (overlay.css):
    • Overlay styling: white background, subtle border and shadow.
    • Large, readable text.
    • Centered over the KaTeX formula.
    • pointer cursor.
  3. Extension declaration manifest.json:
    • Injects content.js, overlay.css and the other scripts.
    • Sets information and permissions of the extension.
  4. Background script background.js:
    • Handles context menu (right click). Needed to display the “Copy as Markdown” option when right clicking the selected text.
  5. Selection script selection-to-markdown.js:
    • A set of functions, workers and utilities to convert HTML to markdown while preserving our extracted LaTeX. Under the hood uses the turndown.js library and the turndown-plugin-gfm.js GitHub-flavored markdown plugin for converting HTML to Markdown.

How to test the extension locally

  1. Create a zip that contains all the files inside the src directory (without containing the src folder itself).
  2. Then go to about:debugging (as if it were an URL) and in the ‘This Firefox’ tab select the button ‘Load a Temporary Add-On…’ and input the zip file.

Chrome version

There is also a Chrome version of this extension: https://github.com/Mapaor/copy-latex-chrome-extension

Acknowledgements

Credits to @leander-ow for his dark mode contribution and to @ashigirl96 for suggesting and providing a working code implementation for the “Copy as Markdown” feature.

This extension also works thanks to the following open source projects:

License

MIT License.

It is MIT Licensed so that anyone can customize it to their needs but please don’t just copy-cat the code and publish it with a new name, it’s weird.

If you have an idea for a new feature open an issue and let me know! Also if you have the time to implement a feature you want it would be great if you made a pull request.

Planned features:

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