Show HN: Firefox in WebAssembly

#1

Post by coolelectronics » Wed, Jul 15, 2026, 9:00 PM UTC

This is the entire Firefox browser rendering to a element. Gecko, all UI components, and the Spidermonkey JS engine are all compiled and running in WebAssembly.

Here are a few things you might find interesting:

- This is fully end to end encrypted! We use the WISP protocol for TCP-over-websockets.

- There is a novel WASM->JS JIT for experimental site speedup

- This port cost over 25k in opus/fable tokens for debugging and JIT research

This was just a fun experiment to push the boundaries of WebAssembly. For a more usable "browser in browser" experience, we also built https://github.com/HeyPuter/browser.js that eats a bit less RAM.

Show HN: Firefox in WebAssembly
developer.puter.com

Re: Show HN: Firefox in WebAssembly

#2

Post by throwaway2027 » Wed, Jul 15, 2026, 9:33 PM UTC

Obligatory https://www.destroyallsoftware.com/talks/the-birth-and-death...

Re: Show HN: Firefox in WebAssembly

#3

Post by mdlxxv » Wed, Jul 15, 2026, 9:33 PM UTC

"Yo dawg. I herd you like web browsers, so I put a browser in your browser, so you can browse the Web while you browse the Web".

Re: Show HN: Firefox in WebAssembly

#4

Post by eqrion » Wed, Jul 15, 2026, 9:36 PM UTC

> There is a novel WASM->JS JIT for experimental site speedup

I would love to see the details for this. SpiderMonkey had an attempted wasm32 JIT backend, but it was never finished.

edit: Apparently it also has some sort of WebAssembly interpreter backend too, which SpiderMonkey doesn't have.

Re: Show HN: Firefox in WebAssembly

#5

Post by ent101 » Wed, Jul 15, 2026, 9:39 PM UTC

mdlxxv wrote: post #3

"Yo dawg. I herd you like web browsers, so I put a browser in your browser, so you can browse the Web while you browse the Web".

should've used this in the splash screen :(

Re: Show HN: Firefox in WebAssembly

#6

Post by rlmineing_dead » Wed, Jul 15, 2026, 9:39 PM UTC

throwaway2027 wrote: post #2

Obligatory https://www.destroyallsoftware.com/talks/the-birth-and-death...

I had this in mind when I first saw this project too LOL

Every year I need to rewatch this talk

Re: Show HN: Firefox in WebAssembly

#7

Post by som » Wed, Jul 15, 2026, 9:45 PM UTC

... doesn't support Firefox mobile apparently :D

Re: Show HN: Firefox in WebAssembly

#8

Post by coolelectronics » Wed, Jul 15, 2026, 9:47 PM UTC

Oh and for anyone asking, you can run firefox-wasm inside firefox-wasm inside firefox! I only got this to load once though since it gets pretty unstable at that level.

Re: Show HN: Firefox in WebAssembly

#9

Post by rlmineing_dead » Wed, Jul 15, 2026, 9:49 PM UTC

som wrote: post #7

... doesn't support Firefox mobile apparently :D

Does firefox mobile (Android, since firefox mobile iOS is a WebKit wrapper) support about:config settings? if so you can enable wasm_js_promise_integration in about:config and have it working likely. I will test this on my Pixel 10 pro

Re: Show HN: Firefox in WebAssembly

#10

Post by degamad » Wed, Jul 15, 2026, 9:52 PM UTC

I'm so glad this exists, I've been considering doing something like this for a few months.

I recently got a TV based on VIDAA os, a locked-down linux-based OS where everything is rendered from Web pages. It has a built-in browser that doesn't support ad-blocking (I suspect VIDAA is profiting from showing ads on the TV), and you can't install new apps unless they're Web pages.

This would hopefully allow one to run Firefox within the existing browser, then install uBlock Origin within Firefox... I know what this weekend's project is going to be...