Unable to run on firefox using your demo URL

**Describe the bug**
When trying to run ffmpeg.wasm on firefox on my own site I ran into an error saying `f.asm` is undefined. This also reproduces on the provided demo site https://ffmpegwasm.et.r.appspot.com/.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to https://ffmpegwasm.et.r.appspot.com/
2. Upload a video
3. Open console
4. See error: TypeError: f.asm is undefined

**Expected behavior**
The video should convert properly

**Desktop (please complete the following information):**
- OS: Windows
- Browser Firefox