Custom browser extensions for Chrome, Firefox, Safari and Edge
Gjethe builds browser extensions on Manifest V3 for Chrome, Edge, Firefox and Safari: productivity tools, e-commerce helpers, AI assistants, CRM connectors and private tools for company teams. We design the popup and options pages, request only necessary permissions, build any backend the extension needs and handle store submission. Pricing is based on your project and agreed in your quote.
- Free first consultation
- Written quote for your project
- Flexible payment milestones
At a glance
- Standard
- Manifest V3
- Browsers
- Chrome, Edge, Firefox, Safari
- Distribution
- Public, unlisted or company-only
- Pricing
- Quoted per project
Definition
What is browser extensions?
A browser extension is a small program that adds features to a web browser (reading or changing web pages, adding buttons to the toolbar, or connecting the browser to other services) built with web technologies and distributed through browser extension stores.
Extensions live exactly where people already work: inside their browser, on top of the sites they use all day. That makes them ideal for saving clicks, filling in data, capturing information, adding AI to any text box or connecting a web app to your CRM. It also means users trust them with a lot, so we design for minimal permissions, clear privacy disclosures and smooth store review.
Who is it for?
Founders with an extension product
The extension is the product: a productivity tool, shopping helper or AI assistant sold to the public.
SaaS companies
A companion extension brings your product into the tools your users already work in.
Internal teams
A private extension automates repetitive steps in the web tools your staff use every day.
E-commerce and affiliate businesses
Price comparison, coupon, wishlist and product research tools.
What's included, and what you keep
What's included
- Use-case and permission planning
- Popup, side panel and options page design
- Manifest V3 development in TypeScript
- Content scripts for reading or enhancing web pages
- Background service worker logic
- Storage and sync of user settings
- Authentication with your web app or OAuth
- Backend API when the extension needs one
- Cross-browser builds for Chrome, Edge and Firefox
- Safari packaging through Xcode when needed
- Privacy policy and store listing assets
- Store submission and review
What you receive
Handed over at the end. Yours to keep.
- Published extension under your developer account
- Source code and build scripts
- Store listings with screenshots and descriptions
- Privacy documentation for reviewers
- Update and release instructions
What kinds of extensions do we build?
AI assistants
Summarise pages, draft replies, translate or rewrite text anywhere in the browser.
CRM and sales tools
Capture leads from websites and send them to HubSpot, Salesforce or your own system.
Shopping helpers
Price tracking, comparison and wishlist tools for e-commerce sites.
Internal productivity tools
Auto-fill repetitive forms, add shortcuts and enforce checks in internal web systems.
Why permissions matter so much
Every permission an extension requests is shown to users at install time and examined during store review. Broad permissions such as access to all websites trigger stricter review, deter installs and raise the stakes if anything goes wrong.
We design extensions to request the narrowest permissions possible, specific sites instead of all sites, optional permissions requested only when a feature needs them, and active-tab access instead of permanent access where it works. The result is an extension that's easier to approve, easier to trust and safer to run.
Manifest V3 in plain terms
| Concept | What it means for your extension |
|---|---|
| Service worker | Background logic runs only when needed instead of constantly, saving memory |
| Declarative rules | Network filtering uses predefined rules rather than inspecting every request |
| No remote code | All code ships inside the extension package, which reviewers can inspect |
| Granular permissions | Access can be limited to specific sites or granted at the moment it's needed |
How browser extensions works, step by step
Every step has a clear output you can review. Timing is agreed in your quote.
- 1
Concept and permissions
What the extension does, on which sites, and the minimum permissions required.
- 2
UX design
Popup, side panel and in-page elements designed to fit naturally into the sites they enhance.
- 3
Build
Manifest V3 development with test builds you can load in your browser.
- 4
Backend
Accounts, sync or AI APIs set up when the extension needs a server.
- 5
Cross-browser testing
Chrome, Edge and Firefox tested; Safari packaged if required.
- 6
Store submission
Listings, privacy disclosures and submission, with responses to any reviewer questions.
Tools, and what shapes your quote
Pricing is based on your project and agreed in your quote. These are the things that move it.
| Factor | Why it matters |
|---|---|
| Number of sites supported | Content scripts that work on many different websites need more handling and testing. |
| Backend requirements | Accounts, sync, payments or AI processing need a server. |
| Browser coverage | Safari packaging and testing adds work beyond Chromium browsers and Firefox. |
| UI complexity | A simple popup is quicker than a full side-panel application. |
| Monetisation | Licences, subscriptions or usage limits require billing and account logic. |
| Area | Tools |
|---|---|
| Extension | Manifest V3, TypeScript, WebExtensions API, chrome.storage |
| UI | React, TailwindCSS, side panel API |
| Build | Vite, WXT or Plasmo, Xcode for Safari |
| Backend | Node.js, Supabase, OAuth, AI APIs |
Common mistakes to avoid
What we see go wrong most often, and how a good project avoids it.
Requesting access to all websites
Broad permissions slow review and scare users. Request only the sites and access the feature needs.
Relying on fragile page selectors
Websites change their markup. Content scripts need resilient selectors and monitoring for breakage.
No privacy policy
Extensions handling user data need a clear privacy policy and accurate store disclosures.
Forgetting updates
Browser and website changes break extensions over time; plan for maintenance.
Frequently asked questions
What is Manifest V3?
Manifest V3 is the current extension platform required by the Chrome Web Store. It uses service workers instead of background pages and tighter permissions. Every extension we build targets it.
Can one extension work in Chrome, Firefox, Edge and Safari?
Mostly, yes. Chrome and Edge share an engine, Firefox supports the same WebExtensions API with small differences, and Safari needs an Xcode wrapper and an Apple developer account, which we handle.
Can the extension be private to my company?
Yes. Extensions can be published as unlisted or deployed privately to your organisation's managed browsers instead of the public store.
Can an extension use AI?
Yes. The extension sends text to an AI API through your backend, so API keys stay secret and usage can be limited per user.
Why was my extension rejected?
Common reasons are excessive permissions, unclear purpose, missing privacy disclosures or code that can't be reviewed. We fix the cause and resubmit.
Can you take over an existing Manifest V2 extension?
Yes. We migrate it to Manifest V3, replacing background pages with a service worker and updating any network-filtering logic.
Can the extension sync with our web app?
Yes, through your app's login and API, so users see the same data in both.
Can we charge for the extension?
Yes, through your own subscription or licence system connected to a payment provider such as Stripe.
Who owns the developer account?
You do. The extension is published under your Chrome Web Store, Firefox and Apple accounts.
How long does Chrome Web Store review take?
It varies with the extension's permissions and complexity, and Google doesn't publish a fixed schedule. Narrow permissions and complete privacy disclosures make reviews smoother.
Can the extension work on our internal web tools?
Yes. Content scripts can enhance internal systems (adding buttons, checks or auto-fill) without changing those systems themselves.
How do users get updates?
Published updates install automatically in users' browsers after store review, so everyone stays on the latest version.
Can the extension work offline?
Parts can. Settings and saved data live in extension storage, and features that don't need a server keep working; anything calling an API waits for a connection.
Do you maintain extensions after launch?
Yes. Websites change their layouts and browsers update their APIs, so we offer maintenance to fix breakages quickly and keep store listings compliant.
Related services
Web Applications & SaaS
Portals, dashboards and subscription products.
AI API Integration
Language, vision and speech models in your software.
Data Scraping & Extraction
Structured data from websites and documents.
Custom API Development
Documented REST, GraphQL and WebSocket APIs.
Python Automation
Scripts that replace manual reports and data syncing.
Browser Extensions by industry
Build your extension.
Tell us what you need. You get an honest assessment, a clear plan and a written quote. The first consultation is always free.
- What happens next
- 1You tell us what you need
- 2We aim to reply within 24 hours with questions
- 3You get a written quote for your project