Screen not rendering properly on Pale Moon
The screen only appears on gray-and-white, and the mobile gamepad is also shown.

### Screenshots
![wasm4 snake on pale moon](https://user-images.githubusercontent.com/34007063/130713710-261da208-e57c-4047-b0e8-3747bfd17987.png)
[Snake](https://wasm4.org/play/snake) on Pale Moon 29.4.0.2
![wasm4 on pale moon](https://user-images.githubusercontent.com/34007063/130712724-d5123501-32af-4962-9295-b3082813c39e.png)
[Sound Demo](https://wasm4.org/play/sound-demo) on Pale Moon 29.1.1 and 29.4.0.2

I have also been doubting if I should even post this issue as Pale Moon isn't really a popular browser, so this will probably be marked as wontfix, but let's see...