Firefox MCP Server

Instructions

Implementation Reference

• index-multi-debug.js:781-813 (handler)

  The handler function that executes the get_performance_metrics tool. It retrieves performance timing, paint events, and memory usage from the browser page using Playwright's evaluate method on the Performance API.

  async getPerformanceMetrics(args = {}) {
    const { tabId } = args;
    const effectiveTabId = tabId || this.activeTabId;
    const page = this.getPage(effectiveTabId);
    
    // Get performance metrics from browser
    const metrics = await page.evaluate(() => {
      const nav = performance.getEntriesByType('navigation')[0];
      const paint = performance.getEntriesByType('paint');
      
      return {
        navigation: nav ? {
          domContentLoaded: nav.domContentLoadedEventEnd - nav.domContentLoadedEventStart,
          loadComplete: nav.loadEventEnd - nav.loadEventStart,
          totalTime: nav.loadEventEnd - nav.fetchStart
        } : null,
        paint: paint.map(p => ({ name: p.name, startTime: p.startTime })),
        memory: performance.memory ? {
          usedJSHeapSize: performance.memory.usedJSHeapSize,
          totalJSHeapSize: performance.memory.totalJSHeapSize,
          jsHeapSizeLimit: performance.memory.jsHeapSizeLimit
        } : null,
        timestamp: Date.now()
      };
    });
  
    return {
      content: [{
        type: 'text',
        text: `Performance Metrics:\n` + JSON.stringify(metrics, null, 2)
      }]
    };
  }

• index-multi-debug.js:325-334 (registration)

  Registration of the get_performance_metrics tool in the ListToolsRequestSchema handler, including name, description, and input schema specifying optional tabId.

  {
    name: 'get_performance_metrics',
    description: 'Get performance metrics (timing, memory usage)',
    inputSchema: {
      type: 'object',
      properties: {
        tabId: { type: 'string' }
      }
    }
  },

• index-multi-debug.js:325-334 (schema)

  Input schema definition for the get_performance_metrics tool, defining optional tabId parameter.

  {
    name: 'get_performance_metrics',
    description: 'Get performance metrics (timing, memory usage)',
    inputSchema: {
      type: 'object',
      properties: {
        tabId: { type: 'string' }
      }
    }
  },