Overview
A browser extension sits closer to the user than almost any other piece of software. It is present on every page they visit, has access to the content they are reading, the actions they are taking, and in many cases the data flowing between their browser and the web. That proximity makes browser extensions one of the most powerful tools available for augmenting existing web applications, automating repetitive browser-based workflows, injecting functionality into third-party platforms, and delivering experiences that are simply not possible through a conventional web application.
We build custom browser extensions for Chrome, Firefox, and Edge — from lightweight productivity tools to sophisticated integrations with backend systems, blockchain networks, and enterprise platforms. Every extension we deliver is purpose-built for a specific use case, built to the security standards the proximity to user data demands, and engineered to survive the update cycles and policy changes of the browser extension ecosystem.
What Browser Extensions Can Do
The capabilities available to a browser extension are substantially broader than most people realise. Understanding the full surface area of what is technically possible is the starting point for designing an extension that actually solves the problem rather than working around it:
Content manipulation. Extensions can read and modify the content of any web page the user visits — injecting UI elements, modifying displayed data, highlighting specific content, removing unwanted elements, or overlaying entirely new interfaces on top of existing pages. This makes extensions the right tool when you need to add functionality to a third-party web application you do not control.
Network interception. Extensions can intercept, inspect, modify, block, and redirect network requests made by the browser — enabling ad blocking, request rewriting, API response modification, and traffic monitoring at the browser level.
Background processing. Extensions run persistent background service workers that operate independently of any open tab — enabling scheduled tasks, push notification handling, continuous data synchronisation, and event-driven actions that do not depend on the user having a specific page open.
Cross-tab and cross-window coordination. Extensions have visibility across all open tabs and windows, enabling coordination between multiple pages, session state management, and workflow automation that spans multiple web applications simultaneously.
Local storage and synchronisation. Extensions have access to dedicated storage APIs, including Chrome's sync storage that automatically synchronises extension data across all of a user's devices where they are signed into the browser.
Native messaging. Extensions can communicate with native desktop applications running on the user's machine through the native messaging API — enabling browser-to-desktop integration that bridges web and local application contexts.
Crypto and blockchain integration. Browser extensions are the standard delivery mechanism for crypto wallets and Web3 interfaces. Extensions can inject provider objects into web pages, handle transaction signing requests, manage key material securely in the extension's isolated storage, and interact with blockchain networks directly from the browser context.
Use Cases We Build For
Crypto wallets and Web3 interfaces Browser extensions are the canonical form factor for non-custodial crypto wallets — MetaMask being the most recognised example. We build custom wallet extensions that manage key material, handle EIP-712 typed data signing, process transaction requests from dApps, connect to EVM networks and Solana, and expose a standard provider interface that existing Web3 applications can interact with natively.
Trading and market data tools For traders who work primarily in the browser — on exchange interfaces, charting platforms, or custom dashboards — we build extensions that augment these interfaces with additional data, automate repetitive order entry workflows, display real-time data overlays, or bridge browser-based platforms with desktop trading applications.
Enterprise productivity and workflow automation Many enterprise workflows involve repetitive actions across web-based tools — copying data between a CRM and an ERP, filling forms with data from internal systems, triggering backend processes from within third-party SaaS platforms. We build extensions that automate these workflows, reducing manual effort and eliminating transcription errors between systems.
Data extraction and monitoring For applications that need to consume data from web sources that do not provide an API, browser extensions provide a structured way to extract and forward that data to backend systems — with the full rendering context of the browser available, handling JavaScript-rendered content that server-side scrapers cannot reach.
Internal tooling overlays Large organisations with complex internal web applications often need to layer additional functionality on top of existing platforms without modifying the underlying system. Extensions enable this — adding custom controls, data validation layers, keyboard shortcuts, or integration triggers to internal tools without touching the source application.
Authentication and security tools Extensions are a natural fit for security tooling — password managers, hardware key integrations, phishing detection, content policy enforcement, and session monitoring all operate effectively at the browser extension layer.
Technical Architecture of a Well-Built Extension
Building a browser extension that is secure, maintainable, and resilient to browser policy changes requires deliberate architectural choices from the start.
Manifest V3 compliance Chrome's Manifest V3 is now the required standard for all new Chrome extensions, with Manifest V2 support being progressively removed. MV3 introduced significant changes to how background processing works — replacing persistent background pages with service workers — and imposed new restrictions on network request modification. We build all new extensions to MV3 standards and can migrate existing MV2 extensions where required.
Content security and isolation Extensions operate in a privileged context with broad access to browser APIs and page content. We apply strict content security policies, minimal permission declarations, and explicit isolation between the extension's own code and the content of pages it interacts with — preventing extension vulnerabilities from becoming page-level security issues.
Permission minimisation The permissions an extension declares are visible to users and reviewed by browser store teams. We declare only the permissions genuinely required for the extension's functionality, with clear justification for each — reducing both user friction at installation and the risk surface if the extension is compromised.
Message passing architecture Communication between an extension's components — content scripts, background service workers, popup UI, and options pages — is handled through a structured message passing system. We design this message architecture explicitly, with typed message schemas and clear ownership of state, rather than building ad-hoc communication that becomes unmaintainable as the extension grows.
Backend integration Most non-trivial extensions need to communicate with a backend. We design the extension-to-backend communication layer with authentication, request signing where sensitive data is involved, and offline-tolerant patterns so the extension degrades gracefully when the backend is unreachable.
Cross-Browser Compatibility
Chrome, Firefox, and Edge all support the WebExtensions API standard, making cross-browser development substantially more achievable than it was historically. We build extensions that target all three browsers from a single codebase where possible, with browser-specific adaptations handled cleanly through capability detection and build-time configuration rather than duplicated codebases.
Safari extension support is available as an additional target where required, though Apple's extension signing and distribution requirements add meaningful overhead to the development and deployment process.
Distribution and Updates
Chrome Web Store — public extensions require store submission and review. We prepare store listings, screenshots, privacy policy documentation, and handle the submission process. For enterprise distribution, Chrome supports policy-based installation that bypasses the public store entirely.
Firefox Add-ons (AMO) — Mozilla's review process differs from Chrome's in meaningful ways. We handle AMO submission and respond to reviewer feedback where extensions require manual review.
Private distribution — for internal enterprise tools that should not be publicly listed, we configure private distribution through browser enterprise policies, allowing extensions to be deployed across an organisation's devices without public store visibility.
Update infrastructure — for self-hosted update distribution outside the browser stores, we build update server infrastructure that serves extension packages and version manifests to deployed installations.
Technologies Used
- TypeScript — all extension logic, type-safe message passing, and background service worker code
- React — popup interfaces, options pages, and injected UI components
- WebExtensions API — cross-browser compatible extension APIs for storage, messaging, tabs, and network interception
- Manifest V3 — current Chrome extension standard, applied to all new extensions
- Webpack / Vite — extension build tooling with multi-target output for different browsers
- Rust / WebAssembly — for performance-critical extension components, cryptographic operations, and wallet key management
- REST / WebSocket — backend communication from background service workers
- EIP-1193 / WalletConnect — standard provider interfaces for Web3 wallet extensions
What to Expect Working With Us
Browser extension projects typically begin with a scoping session where we map the required functionality against what the WebExtensions API makes possible, identify any constraints imposed by the specific websites or platforms the extension will interact with, and define the permission set required. From there we work iteratively — with working builds delivered early so you can validate behaviour in the actual browser environment rather than reviewing specifications.
We maintain extensions after delivery, handling compatibility updates as browsers update their extension APIs, responding to store policy changes that affect approved extensions, and extending functionality as requirements evolve.
Ready to Build Your Extension?
Whether you need a crypto wallet, a workflow automation tool, a trading interface overlay, or something entirely specific to your platform — if it needs to live in the browser, we know how to build it correctly.