firefox - SKILL.md Agent Skill

name: firefox description: Firefox browser automation via WebDriver BiDi. Use when you need to interact with web pages using Firefox, test frontends, or when user interaction with a visible browser is required.

Firefox Browser Tools

Firefox WebDriver BiDi tools for agent-assisted web automation. These tools connect to Firefox running on :9222 with remote debugging enabled.

Setup

Run once before first use:

cd {baseDir}
npm install

Start Firefox

{baseDir}/firefox-start.js                  # Copy user's default profile (cookies, logins)
{baseDir}/firefox-start.js --profile Work   # Copy a named profile (e.g. "Work")
{baseDir}/firefox-start.js --no-profile     # Fresh profile

Launch Firefox with WebDriver BiDi on :9222. By default, copies the user's default profile to preserve authentication state. Use --profile <name> to start with a specific named Firefox profile (as shown in about:editprofile). Use --no-profile for a clean session.

Navigate

{baseDir}/firefox-nav.js https://example.com
{baseDir}/firefox-nav.js https://example.com --new

Navigate to URLs. Use --new flag to open in a new tab instead of reusing current tab.

Evaluate JavaScript

{baseDir}/firefox-eval.js 'document.title'
{baseDir}/firefox-eval.js 'document.querySelectorAll("a").length'

Execute JavaScript in the active tab. Code runs in async context. Use this to extract data, inspect page state, or perform DOM operations programmatically.

Screenshot

{baseDir}/firefox-screenshot.js

Capture current viewport and return temporary file path. Use this to visually inspect page state or verify UI changes.

Cookies

{baseDir}/firefox-cookies.js

Display all cookies for the current tab including domain, path, httpOnly, and secure flags. Use this to debug authentication issues or inspect session state.

Pick Elements

{baseDir}/firefox-pick.js 'Click the close button'
{baseDir}/firefox-pick.js 'Select the upload area'

Ask the user to click on element(s) in the Firefox window. Shows a highlight overlay and banner with instructions. Single click selects one element, Cmd/Ctrl+click to multi-select, Enter to finish, ESC to cancel. Returns element info (tag, id, class, text, html, parents). Use this when you need the user to identify which element to interact with.

Upload Files

{baseDir}/firefox-upload.js '/path/to/file'

Upload a file via the page's file input. Sets up a file chooser listener, clicks the "Upload Files" button, and accepts the file. Use this to upload files through file picker dialogs.

Extract Page Content

{baseDir}/firefox-content.js https://example.com

Navigate to a URL and extract readable content as markdown. Uses Mozilla Readability for article extraction and Turndown for HTML-to-markdown conversion. Works on pages with JavaScript content (waits for page to load).

When to Use

Testing frontend code in a real browser
Interacting with pages that require JavaScript
When user needs to visually see or interact with a page
Debugging authentication or session issues
Scraping dynamic content that requires JS execution
When Firefox-specific behavior is needed