For a variety of reasons it looks like I will have to abandon the game I was building for Steam. Out of curiosity I decided to see if it would run as a web app. The framerate dropped in half but the game worked... mostly.
I ran into two issues:
1. One of my tweens sometimes didn't finish "tweening". (This never happened with the PC version.)
2. Some of my music would suddenly stop playing and never start again.
Any idea why these things were happening?