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Firefox in WebAssembly
- Authors
- Name
- DeepHorus
In a groundbreaking demonstration of web technology, the project Puter has successfully compiled the Firefox browser into WebAssembly, enabling it to run entirely within another browser. Announced on July 16, 2026, this achievement allows users to experience a complete browser inside a browser sandbox, with the team showcasing their own blog running in Firefox within WebAssembly inside Chrome. The project challenges conventional limitations of browser-based computing and highlights the evolving capabilities of WebAssembly.
The developers selected Mozilla's Gecko engine due to its strong single-process support, which simplified the compilation process. To accomplish this, they utilized approximately $25,000 worth of tokens from AI models Claude Opus and Fable, though actual costs were lower thanks to a Claude Max subscription plan. The compiled Firefox can render standard web pages, handle HTTPS connections, and maintain end-to-end encryption.
A critical technical hurdle was the inability of code running in browsers to open arbitrary network connections. Puter solved this by funneling all traffic through their servers using the Wisp protocol, a WebSocket-based proxy. This proxy proved expensive to maintain, with the team scaling servers to handle traffic surges from Hacker News discussions. The proxy does not compromise HTTPS security, as independent inspection confirmed encrypted traffic to HTTPS sites while HTTP traffic remained in cleartext.
"This is absurdly cool," the project's announcement stated, noting the unexpected nature of running one browser inside another. The open-source community has shown keen interest, with the firefox-wasm repository on GitHub attracting attention. A separate project, WebkitWasm by theogbob, compiles WebKit to WebAssembly but currently lacks an accessible online demo.
Looking ahead, this proof of concept could spur further exploration into running complex applications within browser environments. Potential applications include legacy browser compatibility testing, advanced sandboxing, or even running entire operating systems in a browser tab. However, dependency on proxying and high computational costs remain significant barriers to practical deployment. As WebAssembly evolves, such limitations may diminish, making projects like this more feasible. For now, Firefox in WebAssembly stands as an impressive technical showcase that pushes the boundaries of what browsers can do.
