One of these flac files has one more byte of padding than the other. They are otherwise identical. Firefox can play the larger file but not the smaller one. Both play identically in Chrome.

4203 byte file, 3699 bytes of padding:

4204 byte file, 3700 bytes of padding:

Here's a different sound showing the same behavior.

4203 byte file, 73 bytes of padding:

4204 byte file, 74 bytes of padding:

> flac -v
flac 1.4.3

> flac ../fly-on-the-wall/boing.flac -P 3699 -o 1-4203.flac
> flac ../fly-on-the-wall/boing.flac -P 3700 -o 1-4204.flac 
> flac ../fly-on-the-wall/ball-fall.flac -P 73 -o 2-4203.flac
> flac ../fly-on-the-wall/ball-fall.flac -P 74 -o 2-4204.flac