---
title: "Firefox Compiled to WebAssembly, Runs Inside a Browser"
source: "Simon Willison 博客（Atom）"
source_tier: "t2"
url: "https://simonwillison.net/2026/Jul/16/firefox-in-webassembly/#atom-everything"
permalink: "https://feed.astralor.com/items/itm_a798d725b35edc5e74a4e5bc"
published: "2026-07-16T23:34:16.000Z"
score: 71
channel: "tech"
tags: ["ai-assisted-programming","Claude","Firefox","Puter","WebAssembly","Wisp Protocol"]
---

# Firefox Compiled to WebAssembly, Runs Inside a Browser

## AI commentary

> This project stunned me: the synergy between AI and WebAssembly can rapidly build complex tasks that previously required extensive human validation. For browser developers, WebAssembly enthusiasts, and AI-assisted programming practitioners, this post deserves thorough reading. After seeing it, I can't help but rethink the boundaries of the browser.

## At a glance

The Puter project has successfully compiled Firefox's Gecko engine to WebAssembly, allowing it to run as a full browser within another browser. The project leveraged AI-assisted programming using Claude Opus and Fable tokens, costing approximately $25,000 via a Claude Max subscription. All network traffic is proxied over WebSocket using the Wisp protocol, with end-to-end encryption support. This breakthrough showcases the immense potential of combining AI with WebAssembly, opening new possibilities for browser nesting and remote operations.

## Key points

- Compiled the Firefox/Gecko engine to WebAssembly, running a full browser instance within a browser.
- The project relied on AI-assisted programming, consuming about $25,000 worth of Claude Opus and Fable tokens.
- All network traffic is proxied via Puter's Wisp protocol WebSocket, with HTTPS encryption support.
- A similar project, WebKitWasm, exists but has no public online demo.

## Full text

Firefox in WebAssembly This is absurdly cool: Puter compiled Firefox to WebAssembly such that the whole browser runs in another browser. Here's my blog, running in Firefox, running in WebAssembly, running in Chrome: They chose Firefox/Gecko because it has strong single-process support. The project took an estimated $25,000 of Claude Opus and Fable tokens, taking advantage of a Claude Max subscription plan. The demo funnels all traffic over a WebSocket protocol (using the Wisp protocol) through Puter's server - a requirement to get this kind of thing to work because code running in browsers can't open arbitrary network connections. (That proxying sounds expensive! The team had to scale the servers up to handle the traffic during the Hacker News conversation about the project.) Puter claim this supports end-to-end encryption and that looks to be true - I inspected the WebSocket messages and traffic to my own HTTPS site was encrypted whereas requests and responses to http://www.example.com/ were in cleartext. Here's the repo for firefox-wasm. theogbob/WebkitWasm is a similar project that compiles WebKit to WASM, but that one doesn't currently have an accessible online demo. Via Hacker News Tags: browsers, firefox, ai, webassembly, generative-ai, llms, ai-assisted-programming, claude, claude-mythos-fable

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Verify against the original before citing; curated by Astral Feed: https://feed.astralor.com/items/itm_a798d725b35edc5e74a4e5bc