This release adds 3 notable features for engineering teams evaluating rollout.
✓ No known CVEs patched in this version
Topics
Summary
AI summaryNew --connect-existing flag lets you attach MCP to a running Firefox instance preserving cookies and tabs.
Full changelog
What's Changed
New Feature: Connect to existing Firefox (--connect-existing)
You can now attach to an already-running Firefox instance instead of launching a new one. This enables automating your existing browsing session — with cookies, logins, and open tabs intact.
Usage
# Start Firefox with Marionette enabled
firefox --marionette
# Run the MCP server
npx firefox-devtools-mcp --connect-existing --marionette-port 2828
Also supports environment variables: CONNECT_EXISTING=true MARIONETTE_PORT=2828
How it works
- Introduces
GeckodriverHttpDriver— a thin HTTP client that talks to geckodriver's WebDriver REST API directly, bypassing selenium-webdriver's BiDi auto-upgrade (which hangs in connect-existing mode) - Adds
IDriver/IElementinterfaces for compile-time safety across all consumers - BiDi-dependent features (console events, network events) are gracefully skipped in connect-existing mode; all other features work (snapshots, clicks, navigation, screenshots, tab management)
- On close/reset, only the geckodriver process is killed — the user's Firefox stays open
Contributors
- feat: add --connect-existing mode to attach to running Firefox by @rdeknijf-ewx in https://github.com/freema/firefox-devtools-mcp/pull/44
Full Changelog: https://github.com/freema/firefox-devtools-mcp/compare/0.7.4...0.8.0
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About freema/firefox-devtools-mcp
Firefox browser automation via WebDriver BiDi for testing, scraping, and browser control. Supports snapshot/UID-based interactions, network monitoring, console capture, and screenshots.
Related context
Beta — feedback welcome: [email protected]