Firefox MCP Server

Instructions

Implementation Reference

• index-multi-debug.js:1382-1398 (handler)

  The handler function that implements the start_monitoring tool. It sets up page monitoring listeners for console, errors, network based on types, injects WebSocket monitoring if requested, and returns a confirmation message.

  async startMonitoring(args) { 
    const { tabId, types = ['console', 'errors', 'network', 'websocket'] } = args;
    const effectiveTabId = tabId || this.activeTabId;
    const page = this.getPage(effectiveTabId);
    
    if (types.includes('console') || types.includes('errors') || types.includes('network')) {
      await this.setupPageMonitoring(page, effectiveTabId);
    }
    
    if (types.includes('websocket')) {
      await this.injectWebSocketMonitoring(page, effectiveTabId);
    }
    
    return {
      content: [{ type: 'text', text: `Monitoring started for tab '${effectiveTabId}': ${types.join(', ')}` }]
    };
  }

• index-multi-debug.js:338-348 (schema)

  Input schema for validating arguments to the start_monitoring tool, defining tabId and optional types array.

  inputSchema: {
    type: 'object',
    properties: {
      tabId: { type: 'string' },
      types: {
        type: 'array',
        items: { type: 'string', enum: ['console', 'errors', 'network', 'websocket', 'performance'] },
        default: ['console', 'errors', 'network', 'websocket']
      }
    }
  }

• index-multi-debug.js:449-450 (registration)

  Registration in the tool dispatch switch statement within the CallToolRequestSchema handler, routing calls to start_monitoring to the startMonitoring method.

  case 'start_monitoring':
    return await this.startMonitoring(args);

• index-multi-debug.js:335-349 (registration)

  Tool registration object in the ListToolsRequestSchema response, defining name, description, and schema for start_monitoring.

  {
    name: 'start_monitoring',
    description: 'Start/restart monitoring for a tab',
    inputSchema: {
      type: 'object',
      properties: {
        tabId: { type: 'string' },
        types: {
          type: 'array',
          items: { type: 'string', enum: ['console', 'errors', 'network', 'websocket', 'performance'] },
          default: ['console', 'errors', 'network', 'websocket']
        }
      }
    }
  },

• index-multi-debug.js:485-540 (helper)

  Helper function called by start_monitoring to set up console, JS error, network, and WebSocket monitoring event listeners on the page.

  // Setup monitoring listeners for a page
  async setupPageMonitoring(page, tabId) {
    console.error(`Setting up monitoring for tab: ${tabId}`);
  
    // Console monitoring
    page.on('console', (msg) => {
      const logs = this.consoleLogs.get(tabId) || [];
      logs.push({
        type: msg.type(),
        text: msg.text(),
        location: msg.location(),
        timestamp: Date.now()
      });
      this.consoleLogs.set(tabId, logs);
    });
  
    // JavaScript error monitoring
    page.on('pageerror', (error) => {
      const errors = this.jsErrors.get(tabId) || [];
      errors.push({
        message: error.message,
        stack: error.stack,
        timestamp: Date.now()
      });
      this.jsErrors.set(tabId, errors);
    });
  
    // Network monitoring
    page.on('request', (request) => {
      const activity = this.networkActivity.get(tabId) || [];
      activity.push({
        type: 'request',
        url: request.url(),
        method: request.method(),
        headers: request.headers(),
        resourceType: request.resourceType(),
        timestamp: Date.now()
      });
      this.networkActivity.set(tabId, activity);
    });
  
    page.on('response', (response) => {
      const activity = this.networkActivity.get(tabId) || [];
      activity.push({
        type: 'response',
        url: response.url(),
        status: response.status(),
        headers: response.headers(),
        timestamp: Date.now()
      });
      this.networkActivity.set(tabId, activity);
    });
  
    // Inject WebSocket monitoring
    await this.injectWebSocketMonitoring(page, tabId);
  }