Jenny Wilson 
If you are starting a browser extension SaaS, you need a backend for auth, data storage, and Stripe webhook handling. Supabase and Firebase are the two options that come up in every serious conversation — both give you auth, a database, and serverless functions in one platform without running your own infrastructure.
They are not interchangeable. Here is what actually matters when choosing between them for an extension backend.
The Core Difference
Firebase is Google’s full-stack backend platform. It uses NoSQL document storage (Firestore), has deep integration with Google’s ecosystem, and has been production-hardened since 2014. The client SDKs are mature and the platform is extremely reliable.
Supabase is an open-source Firebase alternative built on PostgreSQL. It offers a SQL interface over your data, REST and Realtime APIs generated directly from your schema, and Edge Functions (Deno runtime). It launched in 2020 and has grown rapidly.
The architectural decision comes down to one question: do you want a document database or a relational database?
Auth
Both platforms handle extension auth well. The auth flow in a browser extension has a few extension-specific constraints:
- The popup cannot reliably keep a session in localStorage (popup storage is isolated from the tab’s web page context)
- The background service worker has a different storage context from the popup
- You typically want auth state shared across the popup, content scripts, and the dashboard app
Firebase Auth: Mature, battle-tested. The Firebase SDK handles token refresh automatically. Persisting the session across extension contexts requires explicit work — you need to serialize the Firebase user token and share it via chrome.storage. The Firebase Auth session does not automatically work across the popup and service worker without wiring.
Supabase Auth: The Supabase client requires a custom storage adapter to persist auth state to chrome.storage instead of localStorage. This is a few lines of code but it must be done correctly. Supabase’s JWT-based auth makes it straightforward to verify sessions server-side in Edge Functions.
Both require extension-specific session management code. LightningAddon ships this for both backends as adapters implementing a ClientAuth interface — the application code is identical regardless of which backend you choose.
Database
Firestore (Firebase): Document-oriented. Fast to get started. Flexible schema. Real-time subscriptions built in. Scales easily without any schema design work. The query model is limited — no joins, complex queries require denormalization, and queries against multiple collections require multiple round trips.
Supabase (PostgreSQL): Relational. Requires schema design upfront. Row Level Security policies control access directly in the database. SQL means you can write complex queries, joins, and aggregations without restructuring your data. The Realtime API enables subscriptions to row-level changes.
For most browser extension SaaS products, the data model is simple enough that this distinction does not matter much early on: a users table, a subscriptions table, maybe a usage table. Both databases handle this trivially.
Where the difference shows up is at scale or complexity: if your product needs to query across multiple dimensions, report on usage, or analyze behavioral data, SQL is dramatically easier to work with than Firestore’s denormalized document model. If you already know SQL, Supabase will feel natural. If you have primarily worked with document databases, Firestore will feel natural.
Serverless Functions
Both platforms offer serverless function runtimes for your Stripe webhook handler and any server-side logic you need.
Firebase Cloud Functions: Node.js runtime. Familiar environment. Cold start times can be slow for infrequently called functions (relevant if your Stripe webhooks come in bursts). Deployed with the Firebase CLI.
Supabase Edge Functions: Deno runtime with TypeScript built in. Deployed globally at the edge, so latency is low regardless of where your users are. Cold start times are fast. The Deno runtime has a slightly different module system from Node.js — most npm packages work, but you may encounter occasional compatibility issues.
For Stripe webhook handling (which needs to respond within 30 seconds), both are fast enough. Edge Functions win on latency; Cloud Functions win on ecosystem compatibility.
Cost
Both platforms have generous free tiers. At scale, the cost profiles differ:
Firebase: Firestore charges per read/write operation. A dashboard that loads user data can consume many reads quickly. Costs can grow non-linearly if you are not careful about your query patterns. Cloud Functions are billed per invocation and compute time.
Supabase: Database storage and compute are billed primarily by database size and query volume. Edge Function invocations are cheap. The PostgreSQL query model means you can do more work per query, which often means fewer total queries for the same result.
At the scale of a typical indie extension SaaS (under 1,000 paying users), both are effectively free. The cost difference becomes meaningful at larger scale.
Which One to Choose
Choose Firebase if:
- You have existing Firebase experience or your team does
- You want the most mature, proven auth SDK available
- You are building something where real-time collaboration is central (Firestore real-time is best in class)
- You want Google’s reliability guarantees
Choose Supabase if:
- You are comfortable with SQL or want to learn it
- You want open-source infrastructure with the option to self-host later
- Your product will have complex data querying needs
- You prefer a more conventional relational data model
Neither is wrong. The productivity gain from using a familiar technology often outweighs the technical differences between them.
How LightningAddon Handles Both
LightningAddon ships both Firebase and Supabase backends with full feature parity. Auth, Stripe webhook handling, storage, and cloud functions are implemented for both. The VITE_BACKEND environment variable switches between them — no application code changes required.
This means you can start with one, ship a real product, and switch later without a rewrite if you change your mind. More practically, it means you can evaluate both in a working context rather than from blog posts and documentation.
The backend adapters for both live in apps/firebase and apps/supabase in the monorepo. Reading the implementation side-by-side is the best way to understand the practical differences — not theoretical comparisons, but actual code doing the same thing two different ways.
