Carbon Visualiser for Firefox

A Firefox browser extension that tracks real-time CPU utilisation and network activity across browser tabs, then converts those measurements into estimated carbon emissions using regional carbon intensity data.

Why This Exists

Web browsing consumes energy, but the environmental cost is invisible to users. End-user devices account for roughly 51% of streaming-related emissions (Carbon Trust, 2021), yet no browser-native tool exists to measure this impact in real time.

This extension bridges that gap by accessing system-level metrics through Firefox's privileged WebExtension APIs, something standard extensions cannot do. It captures per-process CPU time via ChromeUtils.requestProcInfo() and per-request network transfer sizes via the Performance API, then applies empirical conversion factors and live carbon intensity data to estimate CO₂ emissions.

What It Does

• Tracks CPU time per browser tab using Firefox's internal process monitoring
• Captures network transfer sizes and timing for every request (no DevTools required)
• Converts measurements to energy consumption using the Boavizta API
• Applies real-time carbon intensity data from the UK Carbon Intensity API
• Displays per-session carbon breakdown (device vs. network) in a sidebar panel
• Runs entirely client-side with no external server dependency

Demo

Architecture

All data collection and processing runs within the extension:

Content Script (PerformanceObserver)
    ↓ network timing + transfer sizes
Background Script (Aggregation Service)
    ← CPU metrics (ChromeUtils.requestProcInfo)
    ← Carbon intensity (Carbon Intensity API)
    ← Device power profile (Boavizta API)
    ↓ CO₂ estimates
Sidebar UI (React)

The extension makes no requests to any server controlled by the developer. The only external calls are to public carbon/energy APIs (Boavizta, UK Carbon Intensity).

Privileged API Usage

The extension uses experiment_apis for read-only access to browser internals:

API	Purpose	Access Pattern
ChromeUtils.requestProcInfo()	Per-process CPU time and memory	Read-only
Services.wm.getEnumerator()	Tab-to-process mapping via outerWindowID	Read-only

No browser state is modified. No user data leaves the browser.

Installation

Requirements

• Firefox Developer Edition or Nightly
• In about:config, set:
  • xpinstall.signatures.required → false
  • extensions.experiments.enabled → true

Setup

git clone https://github.com/Audio431/carbon-visualiser-xpi.git
cd carbon-visualiser-xpi/cost-model-addon
npm install
npm run build

Load the extension in Firefox:

1. Open about:debugging#/runtime/this-firefox
2. Click "Load Temporary Add-on"
3. Select cost-model-addon/dist/manifest.json

Running Tests

npm test

Carbon Calculation Methodology

The emission estimates follow the methodology described in the accompanying dissertation (University of Glasgow, 2025).

CPU emissions (Equation 5.1): E_CPU = T_CPU × P_device × 10⁻³

Where T_CPU is total CPU time in hours and P_device is device power consumption in watts, sourced from the Boavizta API.

Network emissions (Equation 5.2): E_network = T_wait × P_datacenter + D_size × E_transmission

Where D_size is total data transferred and E_transmission is 0.065 kWh/GB for fixed-line broadband (Aslan et al., 2018).

Total CO₂ (Equation 5.3): CO₂e = (E_CPU + E_network) × CI_region

Where CI_region is the regional carbon intensity in gCO₂e/kWh.

Current Scope and Limitations

• CPU power profile is currently configured for Apple M1; configurable device support is planned
• Carbon intensity data uses the UK Carbon Intensity API; global coverage via Electricity Maps is planned
• Network timing for cross-origin resources without Timing-Allow-Origin headers will have zeroed timing fields
• Content scripts cannot inject on privileged pages (about:*)

Migration Status

This extension was originally built with a client-server architecture (dissertation version, March 2025). The following changes have been made:

Component	Before	After
Network capture	DevTools onRequestFinished (required DevTools open)	PerformanceObserver in content script
Data aggregation	External Node.js server via WebSocket	Local background script
Carbon calculation	Server-side	Client-side
External server	Required (Render deployment)	None
DevTools dependency	Required	Removed

Legacy server code remains in cost-estimation-server/ with a dontbuild marker. Removal is pending final validation.

Roadmap

• Remove legacy DevTools and WebSocket code
• Auto-stop tracking on sidebar close
• Configurable device power profiles (replace hardcoded M1)
• Global carbon intensity via Electricity Maps API
• Timer-based tracking UI
• Per-tab emissions breakdown in real time
• Privileged signing exploration with Mozilla

License

Mozilla Public License 2.0