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firefox-bidi-mcp

firefox-bidi-mcp

by XuanZhiYouXuan2025
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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Open or close Responsive Design Mode (RDM)

browser_responsive_mode

Open, close or query Firefox Responsive Design Mode for a tab. MEASURED details that matter: (1) the entry point is ResponsiveUIManager.openIfNeeded(window, tab, {trigger}) from module "devtools/client/responsive/manager" — that module IS…

Instructions

Open, close or query Firefox Responsive Design Mode for a tab. MEASURED details that matter: (1) the entry point is ResponsiveUIManager.openIfNeeded(window, tab, {trigger}) from module "devtools/client/responsive/manager" — that module IS the manager instance, not a container; (2) the window argument MUST come from Services.wm.getMostRecentWindow("navigator:browser"); passing gBrowser.ownerGlobal through the DevTools loader fails with "can't access property gBrowser, window is undefined"; (3) the manager must be cached on the chrome window — a fresh DevToolsLoader cannot see a UI opened through another loader, so closing would silently do nothing. IMPORTANT: iframe.rdm-toolbar is a PERMANENT node in the browser document — it stays after closing, so never use its presence to decide whether RDM is active. Use the responsive-mode class on the browser container (or the manager isActiveForTab) instead.

Input Schema

NameRequiredDescriptionDefault
actionYesWhat to do
contextNoTab (default: the active tab)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

B3.2/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With only readOnlyHint=false declared, the description adds substantial behavioral context: manager caching requirements, silent close failures, and the permanent iframe.rdm-toolbar node. It does not contradict the annotation, but it still omits what status returns and general side effects of opening/closing RDM.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness2/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The purpose is front-loaded, but the body is heavily over-specified with internal module paths and DevTools loader implementation details. Those details do not help an agent select or invoke a simple two-parameter tool and make the description disproportionately long.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The description covers purpose and several behavioral caveats, but with no output schema it should clarify what the status action returns. Usage alternatives are also absent, leaving gaps for a status-capable, mutation-containing tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents both parameters. The description implies tab targeting but does not add meaningful semantics for action values such as toggle or status beyond what the enum provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence states a clear verb set and resource: 'Open, close or query Firefox Responsive Design Mode for a tab.' The resource is distinctive, but the description does not explicitly differentiate it from sibling tools such as browser_set_viewport or browser_devtools_open.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explains operations but gives no guidance on when to choose this tool over alternatives like browser_set_viewport. There are no explicit when/when-not conditions or named sibling tools to route the agent.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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