Fact◆Article

Puter has compiled the entire Firefox browser to WebAssembly, so the whole browser runs inside another browser.

Puter built a project that compiles Firefox itself to WebAssembly, allowing the full browser to run inside another browser like Chrome. ✦ AI generated

Simon Willison · Simon Willison's Weblog · 2026-07-16 · original ↗

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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

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▦ Puter ✳ Chrome ✳ Firefox

Around this claim

Mechanism · 1

The demo must route all network traffic through Puter's server over a WebSocket-based Wisp protocol because code running in a browser can't open arbitrary network connections.Simon Willison · Simon Willison's Weblog · conf 65%

Context · 1

Firefox/Gecko was chosen as the browser to port because it has strong single-process support.Simon Willison · Simon Willison's Weblog · conf 60%

Extends · 1

Building the Firefox-in-WASM project cost an estimated $25,000 worth of Claude Opus and Fable tokens, made feasible by a Claude Max subscription.Simon Willison · Simon Willison's Weblog · conf 65%