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io.github.easonwong-de/firefox-css-theme

Official registry Developer tools

MCP for building, inspecting, and live-debugging Firefox CSS themes.

Source code Documentation

What can you do with io.github.easonwong-de/firefox-css-theme?

  • launch_browser: Launches Firefox with chrome debugging.
  • close_browser: Terminates the browser instance.
  • customize_toolbar: Toggles the Firefox "Customise Toolbar" mode.
  • get_ui_tree: Dumps the hierarchical DOM tree of the selected UI element.
  • query_ui_elements: Queries elements matching a CSS selector in the browser chrome.
  • get_computed_styles: Extracts computed CSS property values of a specific UI element.
  • inject_theme_css: Injects a stylesheet into the live UI.
  • remove_theme_css: Removes an injected stylesheet.

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

NPM package firefox-css-theme
Claude Code 
claude mcp add firefox-css-theme -- npx -y firefox-css-theme@0.3.5 mcp
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "firefox-css-theme": {
            "command": "npx",
            "args": [
                "-y",
                "firefox-css-theme@0.3.5",
                "mcp"
            ]
        }
    }
}

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. Firefox CSS Theme
  2. Getting Started
  3. MCP Server Usage
  4. Available MCP Tools
  5. Commands

Firefox CSS Theme

A toolkit for scaffolding, live-debugging, and installing Firefox CSS themes. For agentic DOM inspection and live styling, an MCP server is also available.

Getting Started

[!TIP] You need Node.js to get started.

For Theme Authors

Scaffold a new theme project using npx:

npx firefox-css-theme create

This interactively prompts for your theme name and stylesheet targets (userChrome only, userContent only, or both).

If you have already opened a theme repository, launch Firefox with live CSS hot-reloading:

npx firefox-css-theme start

[!NOTE] Theme entry files (userChrome.css and/or userContent.css) must be located at the root of the project directory.

For Theme Users

Navigate to the theme directory and install the stylesheets:

npx firefox-css-theme install

The toolkit will look for userChrome.css and userContent.css in the current directory, and install them into the selected Firefox profile.

For the full list of CLI options, run npx firefox-css-theme --help.

MCP Server Usage

The MCP server enables AI assistants to inspect the Firefox chrome DOM, query computed styles, inject custom CSS, and capture UI screenshots in real time.

Configuration

Add the server to your preferred client or development environment:

Claude Code
claude mcp add firefox-css-theme -- npx -y firefox-css-theme mcp
Codex
codex mcp add firefox-css-theme -- npx -y firefox-css-theme mcp
IDE MCP Configuration
{
    "mcpServers": {
        "firefox-css-theme": {
            "command": "npx",
            "args": ["-y", "firefox-css-theme", "mcp"]
        }
    }
}

Available MCP Tools

  • launch_browser: Launches Firefox with chrome debugging.
  • close_browser: Terminates the browser instance.
  • customize_toolbar: Toggles the Firefox "Customise Toolbar" mode.
  • get_ui_tree: Dumps the hierarchical DOM tree of the selected UI element.
  • query_ui_elements: Queries elements matching a CSS selector in the browser chrome.
  • get_computed_styles: Extracts computed CSS property values of a specific UI element.
  • inject_theme_css: Injects a stylesheet into the live UI.
  • remove_theme_css: Removes an injected stylesheet.
  • list_theme_css: Lists all currently injected stylesheets.
  • take_ui_screenshot: Captures a screenshot of a specific UI component.
  • execute_chrome_javascript: Runs JavaScript in the browser chrome window context.

Commands

firefox-css-theme create

Scaffold a new Firefox CSS theme project.

Usage
npx firefox-css-theme create [options]
Options
OptionDescription
-n, --name <name>Theme name
-t, --target <target>Stylesheet target: chrome, content, or both
-f, --forceProceed without warning
firefox-css-theme start

Launch Firefox with live stylesheet bundling and hot-reloading.

Usage
npx firefox-css-theme start [options]
Options
OptionDescription
-b, --binary <path>Path to Firefox executable
-p, --profile <name>Firefox profile name
--headlessRun in headless mode
--atbcStart with Adaptive Tab Bar Colour
--no-toolboxDisable Browser Toolbox
--no-watchDisable file watching
firefox-css-theme install

Install compiled stylesheets from the current working directory into a Firefox profile.

Usage
npx firefox-css-theme install [options]
Options
OptionDescription
-p, --profile <name>Firefox profile name
-m, --mergeMerge with existing stylesheets
-f, --forceProceed without warning

[!WARNING] This operation will overwrite existing CSS themes in the profile unless --merge is specified. A backup is advised.

firefox-css-theme mcp

Start the Model Context Protocol (MCP) server.

Usage
npx firefox-css-theme mcp [options]
Options
OptionDescription
-b, --binary <path>Path to Firefox executable
-p, --profile <name>Firefox profile name

Frequently asked questions

What is io.github.easonwong-de/firefox-css-theme?

MCP for building, inspecting, and live-debugging Firefox CSS themes.

How do I install io.github.easonwong-de/firefox-css-theme?

It runs on your machine. In Claude Code: claude mcp add firefox-css-theme -- npx -y firefox-css-theme@0.3.5 mcp. For other clients, paste the JSON configuration from this page into their MCP settings.

Does io.github.easonwong-de/firefox-css-theme need an API key?

Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.

Is io.github.easonwong-de/firefox-css-theme open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains io.github.easonwong-de/firefox-css-theme?

It is published by easonwong-de. AI.tn lists it but does not maintain or endorse it.

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