This looked really fun, and I tried playing for a couple minutes, but it still was causing a lot of lag for me even if I'm not on Firefox. The music was awesome, and the movement looked nice aside from the lag.
Were you playing on Chrome? There's currently some shader compilation issues that make it stutter a bit on the first play (specifically when the spark particles spawn for the first time and when a power up spawns for the first time) , but if it kept lagging after that's an unknown issue
Brave usually runs it decent. Would recommend giving it another shot since the lag was probably just the shaders compiling, which only cause issues on the first run. If it still has issues I'd like to know more about your hardware specs and OS. Thanks!