Browser Extension Development

What browser extensions are good for

Browser extensions add features to the web browser itself. They can read and modify web pages, add toolbars and side panels, react to user actions and connect to your own systems. That makes them ideal for bringing your product into the places people already work — a CRM sidebar inside Gmail, a research clipper, a pricing tool on supplier websites or a compliance checker on internal apps.

Since Chrome moved to Manifest V3, extensions follow stricter security and performance rules. Building to the current standards from the start avoids rejection from stores and painful rewrites.

Problems we solve

• Users switching constantly between your product and other websites
• Repetitive copy-paste between web apps
• An outdated Manifest V2 extension that needs migrating
• Internal staff needing tools on third-party websites
• Extension store rejections or policy warnings

What’s included

Security and privacy by design

Extensions can see a lot of user data, so stores review them carefully and users are rightly cautious. We request only the permissions the extension needs, limit host access to specific sites where possible, never execute remote code, store tokens securely and explain data use clearly in the store listing and privacy policy. This improves approval rates and user trust.

Building cross-browser

Chrome, Edge, Brave and Opera share the Chromium extension platform; Firefox supports most of the same APIs with some differences; Safari requires packaging inside a native app wrapper. We structure code to share as much as possible, using a common build that outputs a package for each browser and handles API differences in one place.

Anatomy of a modern extension

Modern Chrome, Edge and Firefox extensions use Manifest V3, which changes how extensions are structured compared with older versions:

Because service workers stop when idle, state must be stored deliberately and long-running tasks redesigned — a common source of bugs when porting older extensions.

Publishing and distribution

• Public store listings need clear descriptions, screenshots, a privacy policy and justification for each permission requested.
• Store review can take from hours to several weeks; broad permissions and remote code attract closer scrutiny.
• Private or enterprise distribution lets IT teams force-install internal extensions through Google Workspace, Microsoft Intune or group policies.
• Updates roll out automatically to users, so releases should be tested carefully and staged where the store allows.

We plan permissions with review in mind from the start: requesting only what is needed, using optional permissions where possible and explaining clearly why each one exists.

Testing and maintaining extensions

Extensions run inside websites you do not control, so changes to those sites can break them without warning. We test content scripts against the real target pages, use resilient selectors and fallbacks rather than brittle page structure, and add monitoring that reports errors from users’ browsers. Automated end-to-end tests can load the unpacked extension in Chromium with tools such as Playwright. Browsers also change extension APIs over time, so a small ongoing maintenance budget keeps the extension working through browser updates and store policy changes.

Permissions: asking for as little as possible

Store reviewers and users both judge an extension by the permissions it requests. A warning such as “read and change all your data on all websites” lowers install rates and invites extra review. We design features around narrower options wherever possible: the activeTab permission grants access only when the user clicks the extension, optional permissions are requested at the moment a feature needs them, and host permissions are limited to the specific domains the extension works with.

Exact permission names differ slightly between browsers; we map them per target store.

Store review and listing quality

Each store reviews extensions before publishing them and again after updates. Reviews look at the declared purpose, permissions, privacy practices and whether code is readable. Remote code — JavaScript downloaded and executed at runtime — is not allowed under Manifest V3, so all logic ships inside the package and updates go through review.

• A single, clear purpose described in the listing
• A privacy policy that matches what the extension actually collects
• Readable, non-obfuscated code (minification is fine)
• Accurate screenshots and a short demo video
• Data-use disclosures completed honestly in each store dashboard
• A support contact that answers

Enterprise deployment and management

Extensions built for internal teams are usually deployed through device management rather than public stores. Chrome and Edge support policies that force-install an extension, pin it to the toolbar and push configuration values such as API endpoints or tenant IDs. Firefox and Safari have their own enterprise mechanisms. We build extensions to read managed configuration, so IT teams can roll out one package to every department with different settings.

• Force-installation and update URLs managed by IT
• Managed storage for configuration without user setup
• Single sign-on through your identity provider
• Audit-friendly logging of key actions without capturing page content

Monetisation and licensing options

Browser stores no longer process payments for extensions, so paid extensions handle licensing themselves. The common pattern is a free extension with an account system: users sign in, and features unlock according to a subscription managed through Stripe or a similar provider. Licence checks happen on your server, not in the extension, because anything inside the package can be inspected.

Questions to ask before you build

• Which browsers do your users actually use, and which matter on day one?
• Does the extension need to read page content, or only act when clicked?
• Will it be public, unlisted or deployed only through device management?
• What happens when the websites it works with change their layout?
• Who will handle store review feedback and urgent updates after launch?

Many extensions share code with a progressive web app and are written in TypeScript. To extend your own team, you can hire frontend developers.

Related services

Part of our plugin and extension development services. Often paired with SaaS development.

This page is part of Plugin & Extension Development Services — see the full overview for related services, approach and pricing.