Ironically MS Edge and Chrome work the best for me, FF is pants for some reason
Probably because firefox uses a lot of ram to run compared to other web browsers. I don't know about recent versions - they were supposed to have overhauled it last year or earlier this year to make it less system resource intensive, but I haven't checked it. It used to use about 300-400mb of ram with nothing but the landing/home page open.
* edit: checked. current version of firefox with just the default page open. chrome (not sure which version as I rarely use it) with the default page open. firefox is using around 400-500mb of ram, chrome is using about 100-200mb of ram. You probably also need to take into account that other processes are also using your system resources when playing browser based games compared to desktop games run in fullscreen mode.
question: are you using the preload animation system in VS? if you are, are you manually unloading animations when they are no longer needed?