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Public story · 2026-07-21 · high
The demo doubles as a sandbox blueprint, an isolated browser engine agents could drive without ever touching a host machine.
Why now: Willison posted the demo on July 17, the same week Claude Code's sandbox drew fresh scrutiny.
A project compiles Firefox into WebAssembly and runs it inside Chrome, per Simon Willison's July 17 post. The novelty is fun. The real story is sandboxing. A full browser engine sealed inside a Wasm boundary could let an agent browse the web without ever touching the host machine. That's a complete rendering and JavaScript engine walled off from whatever system it runs inside.
Willison put it simply: "Here's my blog, running in Firefox, running in WebAssembly, running in Chrome."
Agent-driven browsing carries real risk when the agent runs with host-level access instead of a sealed boundary. Claude Code's sandbox and credential disclosures are the concrete reason that risk is getting attention.
Willison's post doesn't say the project was built with agent isolation in mind. It also doesn't address performance, or whether the trick holds outside a demo.
Whether any agent framework actually ships a Wasm-sandboxed browser, rather than just talking about isolation, is the thing worth watching.
Each link below shares sources, entities, or timing with this story.
Claude Code uses MCP / Shared entities / Same source domain / Shared topic / Earlier coverage
Linked by a graph relationship (Claude Code uses MCP); both cover Claude Code, Willison; reported by the same outlet (simonwillison.net).
Simon Willison uses Claude Code / Shared entities / Same source domain / Shared topic / Earlier coverage
Linked by a graph relationship (Simon Willison uses Claude Code); both cover Firefox, WASM, WebAssembly; reported by the same outlet (simonwillison.net).
Simon Willison uses Claude Code / Shared entities / Same source domain / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Simon Willison uses Claude Code); both cover WebAssembly, Willison; reported by the same outlet (simonwillison.net).
Claude Code uses Opus / Shared entities / Same source domain / Shared topic / Earlier coverage
Linked by a graph relationship (Claude Code uses Opus); both cover Claude Code, Willison; reported by the same outlet (simonwillison.net).
Codex competes with Claude Code / Shared entities / Same source domain / Shared topic / Earlier coverage
Linked by a graph relationship (Codex competes with Claude Code); both cover Claude Code, Willison; reported by the same outlet (simonwillison.net).
Claude Code uses Opus / Shared entities / Same source domain / Shared topic / Earlier coverage
Linked by a graph relationship (Claude Code uses Opus); both cover Claude Code, Willison; reported by the same outlet (simonwillison.net).
Simon Willison uses Claude Code / Shared entities / Same source domain / Earlier coverage
Linked by a graph relationship (Simon Willison uses Claude Code); both cover WASM, WebAssembly, Willison; reported by the same outlet (simonwillison.net).
Linked by a graph relationship (Simon Willison uses Claude Code); both cover WASM, WebAssembly, Willison; reported by the same outlet (simonwillison.net).