Firefox DevTools MCP

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 preference values via a privileged API. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.

Get the results collected by a logpoint since it was set.

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 the visible text of the page (document.body.innerText). Caps at maxLength (default 20000 chars); saveTo saves the full text to a file.

Get the source code of a JavaScript file loaded in the page. Requires enable_debugger to have been called.

Hover over element by UID.

Install a Firefox extension using WebDriver BiDi webExtension.install command. Supports installing from archive (.xpi/.zip), base64-encoded data, or unpacked directory.

List console messages, filterable by level, time, text, source. Caps at limit (default 50); saveTo saves all matches to a file.

List downloads tracked since startup, including status and saved file path.

List installed Firefox extensions with UUIDs and background scripts. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.

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 open tabs (index, title, URL). Selected tab is marked.

List privileged (privileged) browsing contexts. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var. Use restart_firefox with env parameter to enable.

List all JavaScript files currently loaded in the page. Requires enable_debugger to have been called.

Navigate history back/forward. UIDs become stale.

Navigate selected tab to URL.

Open new tab at URL. Returns tab index.

Press a single key, optionally with modifiers, to submit, dismiss, navigate or trigger a shortcut. Not for entering text: use fill_by_uid instead.

Print the current page to a PDF file using print CSS. Returns the saved file path.

Check whether the Firefox profiler is currently recording.

Start the Firefox profiler. Provide either a preset name or explicit recording options (entries, interval, features, threads). Cannot combine both. Valid presets: web-developer, firefox-platform, graphics, media, ml, networking, power, debug.

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 a previously set logpoint.

Resolve UID to CSS selector. Fails if the element is gone.

Restart Firefox with different configuration. Allows changing binary path, environment variables, and other options. All current tabs will be closed.

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.

Stop an in-progress screencast recording started with screencast_start and finalize the video file. Returns the path to the saved file.

Capture element screenshot by UID as base64 PNG.

Capture viewport screenshot as base64 PNG. Set fullPage for the whole scrollable document.

Select active tab by index, URL, or title. Index takes precedence.

Select a privileged browsing context by ID and set WebDriver Classic context to "chrome" . Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.

Send a raw WebDriver BiDi command and return its result. Escape hatch for BiDi features no other tool covers; prefer a dedicated tool when one exists.

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 preferences at runtime a privileged API. Requires MOZ_REMOTE_ALLOW_SYSTEM_ACCESS=1 env var.

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.

Control the HTTP cache. Use behavior='bypass' so every request goes to the network — useful for performance measurement and for verifying a change that a cached asset would otherwise hide. Applies to the currently selected tab unless scope='global'. Persists until set back to 'default' or Firefox shuts down.

Set viewport dimensions in pixels.

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 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 a Firefox extension using WebDriver BiDi webExtension.uninstall command. Requires the extension ID returned by install_extension or obtained from list_extensions.

Upload file to file input by UID.