Why does Firefox sometimes throws an error using fread()?

Hi, why does Firefox Desktop/Mobile sometimes throws an error using fread() especially after pressing the refresh button?

```
FILE *file = fopen(filepath.c_str(), "rb");
char buffer[100];
size_t bufferSize = fread(buffer, sizeof(char), sizeof(buffer), file);
```

`exception thrown: RuntimeError: indirect call to null,@http://192.168.0.200/website/plugin/emsc.wasm:wasm-function[721]:0x2306c`

On Chrome, Edge, Opera and Mozilla Nightly it works.

Thanks...