Intent to prototype: WebAssembly SIMD

Summary: Allow Wasm programmers and code generators to use short fixed-length vector data and instructions in applications where those are typically used by native code (media encoders/decoders/processors; numeric kernels). Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1625130 Standard: https

Soft code freeze for Firefox 78 starts May 28

With Firefox 77 RC shipping soon, we are nearing the end of the Nightly 78 cycle. In order to avoid invalidating the testing we get out of late Nightly and to ensure that we can roll out Beta 78 to a wider audience with confidence next week, we'd like to ask that any risky changes be avoided from