Hello, Firefox lover here! The game did run slowly but it wasn't unplayable, and I won't hold my choice of browser against it!
Layla's definitely the strongest, I think! I also like how Kenny can use the recoil of their gun to move around the area quicker. Yasameen... well, I feel like he didn't do enough damage to justify the accuracy of attacks. But that might be in part that he's unlocked right before the giant boss.