Yes, I had the same issue on my old PC with my game for the previous raylib GameJam, I was able to gain around ten FPS by parallelizing some parts of the game update process.
It might seem like overkill for the tasks being parallelized, but it did have a positive effect.
However, with a newer PC today, I no longer experience this problem. Maybe Firefox isn't well optimized for WASM on certain architectures, idk