How do I install the Firefox Devtools Diagnose skill?

Run npx skillmds@latest add mozilla/firefox-devtools-diagnose in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Firefox Devtools Diagnose safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Firefox Devtools Diagnose?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Firefox Devtools Diagnose free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Firefox Devtools Diagnose?

mozilla (@mozilla) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Firefox Devtools Diagnose by mozilla

Name: Firefox Devtools Diagnose
Author: mozilla

File contents

When Firefox DevTools MCP tools are unavailable or the user reports issues with the firefox-devtools-mcp plugin, run this diagnostic sequence automatically. Do not ask the user to do these checks manually.

Diagnostic Steps

1. Check Node.js

Run node --version using the Bash tool.

If the command fails with "command not found": tell the user Node.js is not installed and direct them to download Node.js 20.19.0 or higher from https://nodejs.org.
If the version is below 20.19.0: tell the user their Node.js version is too old and they need to upgrade to 20.19.0 or higher from https://nodejs.org.
If the version is 20.19.0 or higher: Node.js is not the issue, continue to the next check.

2. Check Your Own Tool List

Check whether any firefox-devtools-mcp:* tools are present in your current tool list.

If present: the plugin is installed and connected in this conversation. The reported issue is not a setup problem — investigate the specific tool failure directly (bad arguments, target page state, etc.) rather than continuing this checklist.
If absent: this is ambiguous by itself. An empty tool list looks identical whether the plugin isn't installed, the user is in the Chat tab instead of Cowork, or the plugin is installed in Cowork but failing for some other reason. Do not guess which; continue to the next step.

3. Check Installation and Tab Together

Since an absent tool list can't be attributed to a single cause from your side, ask the user to confirm both of the following in one pass:

Open Customize > Plugins in Claude Cowork and confirm firefox-devtools-mcp appears in the list.
Confirm they are currently in the Cowork tab, not the Chat tab — plugins only work in Cowork.
If the plugin is missing: direct them to the installation steps at https://github.com/mozilla/firefox-devtools-mcp.
If the plugin is present but they were in Chat: ask them to switch to Cowork and retry.
If the plugin is present and they are already in Cowork: continue to the next step.

4. Escalate

If all checks pass and the plugin still does not work, tell the user to report the issue:

File a bug on Bugzilla
Or ask in the #firefox-devtools-mcp Matrix room

---name: firefox-devtools-diagnosedescription: Diagnose Firefox DevTools MCP setup issues. Activate when the firefox-devtools-mcp plugin fails to connect, its tools are not available, or the user reports Firefox DevTools not working in Cowork.---When Firefox DevTools MCP tools are unavailable or the user reports issues with the firefox-devtools-mcp plugin, run this diagnostic sequence automatically. Do not ask the user to do these checks manually.## Diagnostic Steps### 1. Check Node.jsRun `node --version` using the Bash tool.- If the command fails with "command not found": tell the user Node.js is not installed and direct them to download Node.js 20.19.0 or higher from https://nodejs.org.- If the version is below 20.19.0: tell the user their Node.js version is too old and they need to upgrade to 20.19.0 or higher from https://nodejs.org.- If the version is 20.19.0 or higher: Node.js is not the issue, continue to the next check.### 2. Check Your Own Tool ListCheck whether any `firefox-devtools-mcp:*` tools are present in your current tool list.- If present: the plugin is installed and connected in this conversation. The reported issue is not a setup problem — investigate the specific tool failure directly (bad arguments, target page state, etc.) rather than continuing this checklist.- If absent: this is ambiguous by itself. An empty tool list looks identical whether the plugin isn't installed, the user is in the Chat tab instead of Cowork, or the plugin is installed in Cowork but failing for some other reason. Do not guess which; continue to the next step.### 3. Check Installation and Tab TogetherSince an absent tool list can't be attributed to a single cause from your side, ask the user to confirm both of the following in one pass:- Open **Customize > Plugins** in Claude Cowork and confirm `firefox-devtools-mcp` appears in the list.- Confirm they are currently in the **Cowork** tab, not the **Chat** tab — plugins only work in Cowork.- If the plugin is missing: direct them to the installation steps at https://github.com/mozilla/firefox-devtools-mcp.- If the plugin is present but they were in Chat: ask them to switch to Cowork and retry.- If the plugin is present and they are already in Cowork: continue to the next step.### 4. EscalateIf all checks pass and the plugin still does not work, tell the user to report the issue:- File a bug on [Bugzilla](https://bugzilla.mozilla.org/enter_bug.cgi?format=__default__&blocked=2026717&product=Developer%20Infrastructure&component=Firefox%20MCP)- Or ask in the [#firefox-devtools-mcp Matrix room](https://chat.mozilla.org/#/room/#firefox-devtools-mcp:mozilla.org)

Frequently asked questions

Firefox Devtools Diagnose