Atlas / MCP servers / mozilla / Firefox DevTools

Firefox DevToolsSAFE

Name: Firefox DevTools
Author: mozilla

mcp/mozilla/firefox-devtools-1

MCP server by mozilla · claude code · firefox · mcp · Audited 2026-10-03

Model Context Protocol server for Firefox DevTools - enables AI assistants to inspect and control Firefox browser through WebDriver BiDi

Verdict

SAFE

Grade

Trust score

89 /100

Exposed tools

71 40r · 24w · 7d

Transport

stdio

License

NOASSERTION

Stars

456

Overview

From the repository's own README, as read at the audited commit. Badges and raw HTML are left out.

[](https://www.npmjs.com/package/@mozilla/firefox-devtools-mcp) [](https://github.com/mozilla/firefox-devtools-mcp/actions/workflows/ci.yml) [](https://codecov.io/gh/mozilla/firefox-devtools-mcp) [](LICENSE-MIT) [](LICENSE-APACHE)

Model Context Protocol server for automating Firefox via WebDriver BiDi (through Selenium WebDriver). Works with Claude Code, Claude Desktop, Cursor, Cline and other MCP clients.

Repository: https://github.com/mozilla/firefox-devtools-mcp

Note: This MCP server requires a local Firefox browser installation and cannot run on cloud hosting services like glama.ai. Use npx @mozilla/firefox-devtools-mcp@latest to run locally, or use Docker with the provided Dockerfile.

Security

Browser MCP servers carry inherent risks. A few key practices:

Use a dedicated Firefox profile. Never run the server against your regular profile — the agent has access to whatever the browser can reach, including cookies and saved sessions.
Be cautious about which sites you visit. Pages can return content designed to manipulate the agent (prompt injection). Stick to sites you control or trust.
Enable only the tool modules you need. The default basic preset already includes evaluate_script; --tool-preset slim drops it. Higher presets such as --tool-preset developer (debugging, network, console, profiler) and --tool-preset mozilla (privileged cont

Read from source at commit 7134318d871dOBSERVED · 2026-10-03

Connect

Built from this server's own package name, version and transport as found in its source — not copied from anyone's documentation, so it cannot drift against a page we do not control. Replace the environment placeholders with a token scoped to the least it needs.

claude-code (npm)

claude mcp add firefox-devtools-mcp -- npx -y @mozilla/[email protected]

Exposed tools (71)

40 read · 24 write · 7 destructive. Blast radius: 7 tools can delete or overwrite — an agent that can be talked into calling a tool can be talked into calling this one.

Tool	Risk	Description
`accept_dialog`	read	Accept browser dialog. Provide promptText for prompts.
`clear_console_messages`	destructive	Clear collected console messages.
`clear_downloads`	destructive	Clear the tracked downloads buffer.
`clear_snapshot`	destructive	Clear snapshot UIDs. Usually not needed.
`click_by_uid`	write	Click element by UID. Set dblClick for double-click.
`close_firefox_session`	read	Ends the browser session. If the server connected to your existing Firefox,
`close_page`	read	Close tab by index.
`console`	destructive	Read and clear console messages.
`debugging`	write	Inspect scripts and set logpoints (Firefox 153+).
`dismiss_dialog`	read	Dismiss browser dialog.
`downloads`	read	Monitor and manage file downloads.
`drag_by_uid_to_uid`	read	Drag element to another (HTML5 drag events).
`enable_debugger`	write	Enable the JS debugger for the current page. Required before set_logpoint works. Requires Firefox 153+.
`evaluate_privileged_script`	write	Execute JS function in a privileged (chrome) browsing context. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var. Get context ids from list_privileged_contexts.
`evaluate_script`	write	Run a JS function in the page and return its result. Prefer this for targeted reads (a value, text, computed style, whether an element exists) instead of a full take_snapshot. Use the UID interaction tools for clicking, typing, and filling.
`fill_by_uid`	read	Fill text input/textarea by UID.
`fill_form_by_uid`	read	Fill multiple form fields at once.
`get_firefox_info`	read	Get information about the current Firefox instance configuration, including binary path, environment variables, and output file location.
`get_firefox_output`	read	Retrieve Firefox output (stdout/stderr including MOZ_LOG, warnings, crashes, stack traces). Returns recent output from the capture file. Use filters to focus on specific content.
`get_firefox_prefs`	read	Get Firefox preference values via a privileged API. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.
`get_logpoint_results`	write	Get the results collected by a logpoint since it was set.
`get_network_request`	read	Get request details by ID, including the response body (and request body when present). Large text bodies are truncated inline; binary bodies are summarized. URL lookup as fallback.
`get_page_text`	read	Get the visible text of the page (document.body.innerText). Caps at maxLength (default 20000 chars); saveTo saves the full text to a file.
`get_script_source`	read	Get the source code of a JavaScript file loaded in the page. Requires enable_debugger to have been called.
`hover_by_uid`	read	Hover over element by UID.
`input`	read	Interact with the page via UID-based clicks, typing, key presses, drag, and uploads.
`install_extension`	write	Install a Firefox extension using WebDriver BiDi webExtension.install command. Supports installing from archive (.xpi/.zip), base64-encoded data, or unpacked directory.
`launch`	write	Restart Firefox under a different launch configuration.
`list_console_messages`	read	List console messages, filterable by level, time, text, source. Caps at limit (default 50); saveTo saves all matches to a file.
`list_downloads`	read	List downloads tracked since startup, including status and saved file path.
`list_network_requests`	read	List network requests, returning IDs for get_network_request. Filter by url/method/status; caps at limit (default 50); saveTo saves all matches to a file.
`list_pages`	read	List open tabs (index, title, URL). Selected tab is marked.
`list_privileged_contexts`	read	List privileged (privileged) browsing contexts. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var. Use restart_firefox with env parameter to enable.
`list_scripts`	read	List all JavaScript files currently loaded in the page. Requires enable_debugger to have been called.
`management`	read	Inspect Firefox options and logs, and close the browser.
`navigate_history`	read	Navigate history back/forward. UIDs become stale.
`navigate_page`	read	Navigate selected tab to URL.
`network`	read	List and inspect network requests, and control the HTTP cache.
`new_page`	read	Open new tab at URL. Returns tab index.
`pages`	read	Open, navigate, select, and close pages.
`prefs`	write	Get and set Firefox preferences.
`press_key`	write	Press a single key, optionally with modifiers, to submit, dismiss, navigate or trigger a shortcut. Not for entering text: use fill_by_uid instead.
`privileged`	read	Access privileged (
`profiler`	write	Start, stop, and query the performance profiler.
`profiler_is_active`	read	Check whether the Firefox profiler is currently recording.
`profiler_start`	write	Start the Firefox profiler. Provide either a preset name or explicit recording options (entries, interval, features, threads). Cannot combine both. Valid presets: ${VALID_PRESETS.join(
`profiler_stop`	write	Stop the Firefox profiler and save the recorded profile to a file in the downloads directory. Returns the path to the saved file, or null when nothing was saved.
`remove_logpoint`	destructive	Remove a previously set logpoint.
`resolve_uid_to_selector`	read	Resolve UID to CSS selector. Fails if the element is gone.
`restart_firefox`	write	Restart Firefox with different configuration. Allows changing binary path, environment variables, and other options. All current tabs will be closed.
`screencast`	read	Record screencasts of the page viewport (Firefox 154+).
`screencast_start`	write	Start recording a screencast (video) of the current page viewport, saving the output to a file in the downloads directory. Returns a screencast id to pass to screencast_stop. Multiple recordings can run at once.
`screencast_stop`	write	Stop an in-progress screencast recording started with screencast_start and finalize the video file. Returns the path to the saved file.
`screenshot`	read	Capture screenshots of the page or specific elements.
`screenshot_by_uid`	read	Capture element screenshot by UID as base64 PNG.
`screenshot_page`	write	Capture viewport screenshot as base64 PNG. Set fullPage for the whole scrollable document.
`script`	read	Evaluate arbitrary JavaScript in the page context.
`select_page`	read	Select active tab by index, URL, or title. Index takes precedence.
`select_privileged_context`	write	Select a privileged browsing context by ID and set WebDriver Classic context to
`set_download_behavior`	write	Control how downloads are handled: allow (save to a destination folder), deny (cancel), or reset to default. Avoids the native save-file dialog. Requires a recent Firefox.
`set_firefox_prefs`	write	Set Firefox preferences at runtime a privileged API. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.
`set_logpoint`	write	Set a logpoint at a specific location. When execution reaches that line, the expression is evaluated and the result is stored without pausing. Use get_logpoint_results to retrieve collected values. Requires enable_debugger to have been called.
`set_network_cache`	write	Control the HTTP cache. Use behavior=
`set_viewport_size`	write	Set viewport dimensions in pixels.
`snapshot`	read	Capture accessibility/DOM snapshots and resolve UIDs.
`take_snapshot`	read	Capture DOM snapshot with stable UIDs. A UID stays valid across snapshots until its element is removed or the page navigates. Output caps at maxLines (default 100); scope with selector or dump the full tree with saveTo.
`type_text`	read	Type text key by key into the focused element, optionally followed by a key such as Enter. Use fill_by_uid to set the value of a known input; use this for elements that only react to real typing, such as autocomplete fields and rich text editors.
`uninstall_extension`	destructive	Uninstall a Firefox extension using WebDriver BiDi webExtension.uninstall command. Requires the extension ID returned by install_extension or obtained from list_extensions.
`upload_file_by_uid`	write	Upload file to file input by UID.
`utilities`	read	Handle dialogs, history navigation, and viewport sizing.
`webextension`	destructive	Install and uninstall web extensions.

Trust audit

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

Layer	What it checks	Result
L0	Provenance & inventory	PASS
L1	Static analysis of the code	PASS
L2	Instruction surface (what it tells the agent)	PASS
L3	Class-specific surface	WARN
L4	Behavioural (sandbox)	SKIPPED

What the source does

Filesystem: declared (8 observation(s))
Network: declared (4 observation(s))
Shell: declared (5 observation(s))
Dependencies: not all pinned
Secrets in source: none-found

Findings (14)

MEDIUMFilesystem / path · mcp.destructive_tools · CWE-22, CWE-59

clear_console_messages, clear_downloads, clear_snapshot, console, remove_logpoint, uninstall_extension, webextension

Why it matters. 7 tool(s) can delete or overwrite

Fix. prefer a read-only mode or scoped tokens; the page states the blast radius

LOWInventory / provenance · inv.hidden_file · CWE-1104

.codecov.yml

.codecov.yml

Why it matters. hidden member outside the usual dotfiles

Fix. review its purpose

LOWInventory / provenance · inv.hidden_file · CWE-1104

.prettierignore

.prettierignore

Why it matters. hidden member outside the usual dotfiles

Fix. review its purpose

LOWInventory / provenance · inv.hidden_file · CWE-1104

.prettierrc.json

.prettierrc.json

Why it matters. hidden member outside the usual dotfiles

Fix. review its purpose

LOWInsecure crypto · crypto.weak_hash · CWE-327, CWE-338

src/utils/paths.ts:42

const hash = createHash('sha1').update(firefoxPath).digest('hex').slice(0, 8);

LOWInsecure crypto · crypto.weak_hash · CWE-327, CWE-338

tests/utils/paths.test.ts:48

const hash = createHash('sha1').update(binaryPath).digest('hex').slice(0, 8);