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Firefox Devtools Diagnose · mozilla | DecimalAI

agent toolingby mozilla

Firefox Devtools Diagnose

mozilla/firefox-devtools-diagnose

Source mozilla/firefox-devtools-mcp ↗License NOASSERTION

Diagnose Firefox DevTools MCP setup issues.

SkillScore74Maintained

Automatic

Support pack

Last verified 8/21/2026

What it changes

Passed 14 of 19 test cases with the skill, and 3 of 19 without it.

Without skill17%

With skill74%

Checks it passed that the model alone missed

States that Node.js 20.19.0 or higher is required.
Directs the user to upgrade at https://nodejs.org.
Instructs the user to switch to the Cowork tab and retry.

and 13 more in the full report

14 fixed3 passed either way5 still failing1 broke

Pass-rate lift: +57 pp
Tokens: -17%
Agent turns: 0%
Response time: -61%

Model gemini-3.6-flashMeasured 8/21/2026v117 of 23 cases passed with skill · 19 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/mozilla-firefox-devtools-diagnose/SKILL.md https://app.decimal.ai/s/mozilla-firefox-devtools-diagnose/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add mozilla-firefox-devtools-diagnose, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/mozilla-firefox-devtools-diagnose/ and pins it in .decimal/skills.lock

decimalai skills add mozilla-firefox-devtools-diagnose

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/mozilla-firefox-devtools-diagnose/SKILL.md https://app.decimal.ai/s/mozilla-firefox-devtools-diagnose/SKILL.md

Raw file: /s/mozilla-firefox-devtools-diagnose/SKILL.md ↗ · machine-readable summary at /s/mozilla-firefox-devtools-diagnose.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 14 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 14

Prompt

Node.js is v20.19.0, firefox-devtools-mcp is listed under Customize > Plugins, and the user is in Cowork, but tools still fail. What two official support channels should be offered?

What was checked, without and with the skill
Checked	Without skill	With skill
Directs the user to file a bug on Bugzilla under the Developer Infrastructure component.	Missed	Passed
Directs the user to join the #firefox-devtools-mcp Matrix chat room.	Missed	Passed

case-16 · gemini-3.6-flash · 8/21/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md36 linessingle file

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

Track record

Benchmark

14 / 19

test cases passed, vs 3 / 19 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

mozilla / firefox-devtools-mcp

plugins/firefox-devtools-troubleshoot/skills/diagnose/SKILL.md

View on GitHub ↗

License NOASSERTIONImported 8/3/2026Version v1

More skills from the same source and nearby in the registry, with their headline benchmark lift.