my friend asked me to post this comment for her- sometimes when she's digging, the screen turns white. just a lil bug report!
That's definitely a tricky situation. Chromebooks are pretty locked into the Google ecosystem, so switching over to a desktop version of Firefox can be tough. You could try installing the Firefox app from the Google Play Store, it's not quite the same as the desktop version, but it might run a bit more smoothly. If that doesn't help, unfortunately there may not be much else that can be done, since browser games aren't really optimized to take full advantage of device hardware.
Please let your friend know I'm really sorry she had a laggy experience. I genuinely hope Serenitrove can grow enough in the future for me to rebuild it from the ground up in a proper game engine and turn it into a mobile/pc app.