Mozilla SpiderMonkey disables asm.js optimizations by default
Original: Saying goodbye to asm.js
Why This Matters
Marks transition from pioneering asm.js technology to modern WebAssembly standard
Mozilla's SpiderMonkey JavaScript engine disabled asm.js optimizations by default in Firefox 148, with plans to remove the code entirely in future releases. The company recommends migrating to WebAssembly for better performance.
SpiderMonkey announced that asm.js optimizations are disabled by default starting Firefox 148, with complete code removal planned for future releases. Existing asm.js sites will continue functioning as the code runs through regular JavaScript JIT compilation. Mozilla introduced asm.js in Firefox 22 (2013) as a statically-typed JavaScript subset for near-native performance, enabling projects like Unity and Unreal to port C/C++ codebases to web. The Epic Citadel demo was ported in just four days. asm.js proved native-speed web execution was possible and paved the way for WebAssembly, which shipped in Firefox 52. Mozilla cites WebAssembly's success, declining asm.js usage, maintenance costs, and security concerns as reasons for the change. The company recommends recompiling to WebAssembly for faster execution and smaller binaries.