Wasm converts u16 or u8 parameters to u32 types.

So

void foo(u8 param) { ... }
// becomes
void foo(u32 param) { ... }

When calling foo with parameters of type u32, a narrowing conversion is now needed
i.e.

u32 arg = ...;
foo (arg);
//should become
foo((u8)arg);

The RLBox wasm plugin is currently missing this conversion in its ABI fixups

Once fixed, we should also revert the temporary fixes in Bug 1742914 and Bug 1743007