Browser Extensions That Work Inside the Workflow
Browser extension development services by Johnbert Oñez, Philippines. I build Chrome and Firefox extensions using React, TypeScript, and Manifest V3 — productivity tools, AI-powered features, scraping utilities, and SaaS integrations.
The best product tool is the one that appears exactly when the user needs it.
Most software requires users to leave what they are doing, open a separate tab, and context-switch to complete a task. Browser extensions eliminate that gap — they live inside the browsing session and activate in the right moment, on the right page, without breaking the user's flow.
But most extension developers build the happy path and stop there. Poor Manifest V3 compliance, missing permission scoping, broken content scripts on sites with strict CSP, and extensions that get rejected by the Chrome Web Store for avoidable policy violations. Getting extensions right requires experience with exactly those edge cases.
Production-ready extensions built for approval and real-world use.
I design and build browser extensions from concept to published listing. Manifest V3 compliant, permission-minimal, tested on real sites, and submitted with a documentation package that gets through store review. Based in Davao City, Philippines, I deliver remotely with async communication across US, AU, and EU timezones.
- Manifest V3 compliant from the first commit — no last-minute migration headaches
- Permission-scoped to the minimum required — passes security review without friction
- Tested on 50+ real-world sites including sites with strict Content Security Policy
- AI-powered extensions using GPT and Claude API with context-aware prompting
- Chrome Web Store and Firefox AMO submission handled with full listing assets
What I Build For You
Chrome Extensions
Manifest V3 Chrome extensions — popup UI, background service worker, content scripts, storage sync, and Chrome Web Store submission. Production-grade architecture from the start.
Firefox Add-ons
WebExtensions API Firefox add-ons with cross-browser compatibility where needed. Full AMO submission support including listing assets and review documentation.
AI-Powered Extensions
Extensions that integrate GPT-4o or Claude API directly in the browser — page summarizers, writing assistants, research tools, and AI sidebars with context-aware prompting.
Productivity Tools
Extensions that eliminate repetitive browser tasks — form autofill, keyboard shortcuts, custom page modifications, note-taking layers, and workflow automation triggered from within any site.
Content Scrapers
Data extraction extensions that collect structured information from web pages — prices, listings, contact data, and inventory — with scheduling, deduplication, and export to CSV or webhook.
Tab Management
Session management, tab grouping, duplicate detection, tab search, and workspace organization extensions for power users and teams managing complex browser workflows.
Transparent Pricing, No Retainer Required
One-time project fee
A focused single-feature Chrome extension — popup UI, one content script, store submission.
- Single-feature Chrome extension (Manifest V3)
- Popup UI with basic settings panel
- One content script for page interaction
- Chrome Storage sync for preferences
- Chrome Web Store submission assets
- 2 weeks post-launch support
One-time project fee
A multi-feature extension with API integration, settings UI, and cross-browser support.
- Multi-feature extension with background service worker
- Full settings and options page UI
- External API or AI model integration
- Cross-browser Chrome and Firefox support
- Extension analytics via background events
- Chrome Web Store and Firefox AMO submission
- 30 days post-launch support with check-ins
Scoped per project
Team-deployed extensions, enterprise policy management, or complex AI-powered tools.
- Managed enterprise extension deployment
- Chrome Enterprise policy integration
- Backend API and database for shared data
- User authentication and account sync
- Admin dashboard for team configuration
- CI/CD pipeline for extension updates
- Retainer option for ongoing development
From Concept to Published Extension
Extension Scoping
We define what the extension does, which pages it runs on, what permissions it needs, and what the UI looks like. A scoped spec is signed off before any code is written.
Architecture and Permission Design
Extension architecture is designed with Manifest V3 constraints in mind from the start — service worker lifecycle, permission minimization, and CSP compatibility planned before development.
Development and Integration
Extension built with TypeScript and bundled for production. Content scripts, background service worker, popup UI, and any external API integrations developed in parallel cycles with working builds available weekly.
Real-Site Testing
Extension tested against the actual sites and workflows it targets — including sites with strict CSP, single-page applications, and sites that heavily modify the DOM. Edge cases caught before store submission.
Store Submission and Handoff
Chrome Web Store or Firefox AMO submission completed with all required listing assets — screenshots, promotional images, privacy policy, and permission justifications. Source code and documentation delivered.
What Makes These Extensions Actually Publishable
Manifest V3 From the Start
Every Chrome extension is built on Manifest V3 — the current required standard. No legacy MV2 patterns that require migration later, and no service worker lifecycle bugs that only appear in production.
Permission Minimization
Extensions request only the permissions they actually need. Over-permissioned extensions get flagged in store review and trigger user distrust warnings. Minimal permissions are a feature, not an afterthought.
Content Script Robustness
Content scripts are written to handle the full range of sites they run on — strict CSP, dynamically rendered pages, iframes, and single-page app route changes. They do not break on sites you care about.
AI Integration Done Right
AI-powered extensions handle API keys securely via background service worker — never exposed in content scripts. Streaming responses, context length management, and graceful error handling are built in.
Async-First Delivery
Based in Davao City, Philippines (UTC+8). Projects run async-first with Loom demos of working builds and written updates. US, AU, and EU clients get full progress visibility without live meeting scheduling.
Store Submission Handled
Chrome Web Store and Firefox AMO submission is part of every build — including all required listing assets, privacy policy language, and permission justification text that satisfies the reviewer.
Extensions Built, Users Empowered
"We needed a Chrome extension that reads data from third-party sites and pushes it into our app. Three developers had tried and given up because of CSP issues on the target sites. Johnbert scoped the problem correctly, used background fetch to bypass the CSP constraints, and delivered a working extension in three weeks."
"JB built an AI writing assistant extension for us using the Claude API. The sidebar UX is clean, the streaming responses feel instant, and he handled the API key security in a way that actually holds up to scrutiny. We launched on the Chrome Web Store with zero rejection rounds."
"We had an existing MV2 extension that needed to be rebuilt for Manifest V3 without losing functionality. Johnbert did the migration in two weeks and caught three service worker lifecycle bugs that our own team had not detected. The rebuilt extension has been running clean since launch."
Browser Extension Development Questions, Answered
Common questions about this service
Johnbert Oñez
AI Solutions Engineer & Full Stack Developer · 6+ yrs · 50+ projects
Based in Davao City, Philippines. Specialises in production AI systems, full-stack web applications, and WordPress. Remote-first, async-friendly, fixed-fee projects.
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