Thanks for playing! One of my concerns was making the few hidden buttons in the game both not too easy and not too difficult to find, but looks like I may have failed there :( I didn't have any time to let someone else test the game blind before the deadline to check this.
One of the tricks is that they're physically poking out as well, it's not just an adjusted texture. And yeah the music changes as you progress through the game but I can imagine it becoming annoying if things take too long.
What browser issues were you having? I've only tested it in firefox, didn't have time to try other browsers. But I do know webgl can be a bit janky in certain cases so please let me know and I'll adjust the description for future players.