Currently all libraries sandboxed with RLBox + Wasm generate sandboxed code that is included in librlbox.so, however an unsandboxed copy of the code is also included in libxul.so. On platforms where sandboxed code is being used (which should be all supported Firefox platforms soon), there is no reason to duplicate this code for libraries that are only used in their "sandboxed" form. This will lead to reduction in binary size of Firefox.

The Bugbug bot thinks this bug should belong to the 'Core::Javascript: WebAssembly' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Isn't the unsandboxed copy kept for some sandboxed processes?

So there are some libraries like ogg that are used both from a sandboxed and unsandboxed source --- the ogg demuxer is sandboxed, but we leave the ogg decoder unsandboxed (since it is protected by the media process anyway). For this, we would need to keep both versions of the code.
For libraries like graphite, we have sandboxed all uses so we can eliminate the code from libxul and keep just the sandboxed code.