Firefox DevTools MCP (official)
Capped at 70: no passing tool call yet; the tests add up to 100. Why scores are capped
Test points add up to 100; the score is capped at 70 until a tool call passes. Not a quality or security rating. Methodology
Test points before the cap (100/100)
- Install20/20
- Handshake30/30
- Maintenance25/25
- Docs15/15
- License10/10
Transport (tested 2026-10-27): stdio
Score 70/100 · Tools 35 · Token cost ~3,642 · Compare · Last tested 2026-10-27 · Version tested 0.10.6 · Package @mozilla/firefox-devtools-mcp · Repo mozilla/firefox-devtools-mcp
Summary: Firefox DevTools MCP (official) completed an MCP handshake without credentials and exposed 35 tools.
Evidence summary
- Handshake
- pass
- Tools listed
- 35
- Context cost
- 3,642 model-visible tokens (name, description, inputSchema; tiktoken cl100k_base)
Extra payload (sent by the server, usually not read by the model): 231 tokens; raw tools/list total 3,873. Clients differ in what they forward. ranking · add up your servers' context cost - API key
- No key to connect (handshake passed)
- Tested
- 2026-10-27
Test results
| Test | Result | Points | Evidence |
|---|---|---|---|
| install | pass | 20 | npm install @mozilla/firefox-devtools-mcp (Node 20, Linux) succeeded in 4s. |
| handshake | pass | 30 | MCP initialize + tools/list over stdio succeeded with no credentials; 35 tools listed in 1.6s. |
| maintenance | pass | 25 | Repo pushed 0 days before test; 525 GitHub stars. |
| docs | pass | 15 | README over 3,000 chars; install instructions present; mcpServers config example present. Automated check of the package's own README (README shipped in npm package). |
| license | pass | 10 | MIT OR Apache-2.0 (OSI-approved). |
Local-model readiness
Schema context cost: ~3,642 tokens for 35 tools (17,104 bytes) · about 44% of an 8k context. Method: tiktoken cl100k_base over compact JSON of name+description+inputSchema (approximate).
Small-model friendly (schema heuristic, not a model result): unknown.
Small-model task runs: Not yet tested.
What we tested and what we didn't
Tested on 2026-10-27
- Install from the registry
- We connected with no credentials and asked for its tool list: it listed 35 tools (Method details: MCP
initializethentools/list) - Maintenance signals (last push, archived/deprecated status)
- Docs (README length, install and config example)
- License (OSI-approved or not)
- Tool-schema token cost (estimate)
Not tested
- Security: not audited (no code review, no permission or data-flow analysis)
- Real tasks (no functional task runs yet)
- Behaviour with real credentials or a real account
- Performance, rate limits or load
- Correctness of results beyond the listed tasks
Methodology: how we test. A high score means it installs and responds, not that it is safe to give it access to your data.
Known security issues
Not yet checked.
Monthly roundup: MCP security issues, October 2026.
Tool list changes
Baseline recorded from the 2026-10-27 test run; changes appear after the next test.
Snapshot hash (fingerprint of the tool list)
7c126c959b16: SHA-256 of the canonical tool names, descriptions and input schemas. If it changes, the tool list changed.
Raw test record (JSON)
{
"name": "@mozilla/firefox-devtools-mcp",
"version": "0.10.6",
"registry": "npm",
"status": "working",
"tested": "2026-10-27",
"tools_count": 35,
"tools_schema_tokens_est": 3642,
"deprecated": false,
"archived": false,
"tests": {
"install": [
"pass",
20,
"`npm install @mozilla/firefox-devtools-mcp` (Node 20, Linux) succeeded in 4s."
],
"handshake": [
"pass",
30,
"MCP `initialize` + `tools/list` over stdio succeeded with no credentials; 35 tools listed in 1.6s."
],
"maintenance": [
"pass",
25,
"Repo pushed 0 days before test; 525 GitHub stars."
],
"docs": [
"pass",
15,
"README over 3,000 chars; install instructions present; `mcpServers` config example present. Automated check of the package's own README (README shipped in npm package)."
],
"license": [
"pass",
10,
"MIT OR Apache-2.0 (OSI-approved)."
]
}
}Install
npx -y @mozilla/firefox-devtools-mcp
Tools listed
list_pages, new_page, navigate_page, select_page, close_page, get_page_text, take_snapshot, resolve_uid_to_selector, clear_snapshot, click_by_uid, hover_by_uid, fill_by_uid, drag_by_uid_to_uid, fill_form_by_uid, upload_file_by_uid, press_key, type_text, screenshot_page, screenshot_by_uid, print_page, list_downloads, clear_downloads, set_download_behavior, accept_dialog, dismiss_dialog, navigate_history, set_viewport_size, get_firefox_output, get_firefox_info, close_firefox_session, install_extension, uninstall_extension, screencast_start, screencast_stop, evaluate_script
Quick config
{
"mcpServers": {
"firefox-devtools-mcp-official": {
"command": "npx",
"args": [
"-y",
"@mozilla/firefox-devtools-mcp"
]
}
}
}Add to config Opens the config generator with this server selected.
Setup
- Install. Run
npm install @mozilla/firefox-devtools-mcp(Node 20). This is the exact command we ran on 2026-10-27. - Configure. Add the mcpServers entry below to your MCP client config.
- Verify. Restart the client and check that tools/list returns tools (35 in our test).
{
"mcpServers": {
"firefox-devtools-mcp-official": {
"command": "npx",
"args": [
"-y",
"@mozilla/firefox-devtools-mcp"
]
}
}
}Test history
No dated events yet.
FAQ
Is Firefox DevTools MCP (official) deprecated?
No. @mozilla/firefox-devtools-mcp was not deprecated or archived when we last tested it on 2026-10-27.
What replaces Firefox DevTools MCP (official)?
Nothing; Firefox DevTools MCP (official) is not deprecated as of 2026-10-27.
Does Firefox DevTools MCP (official) need an API key?
No. It completed an MCP handshake with no credentials and listed 35 tools.
Embed the badge
Every tested server gets a free embeddable badge. It shows the current score and test date and expires after 90 days. Testing is free; payment never changes a score.