I love this project and have it deployed in my lab! But let it be known that it does have an issue operating on non-Chromium clients. On Chrome, Edge, Brave etc it runs beautifully, but on Firefox there is notable lag/stuttering/crackling.
Based on my research, this is due to how Firefox runs EmulatorJS, as WebAssembly runs slower than on Chromium browsers. This is explained on the EmulatorJS GitHub issue report that I can't link here.
So, not a RomM or even EmulatorJS fault but an issue with the underlying technology (WebAssembly) running in FireFox.