Looks like the Pi 1, 2, and Zero are 32-bit (and probably other old or low spec SBCs). I’m also not sure if Firefox is distinguishing between 32-bit ARM and 32-bit x86.

A point that I haven’t seen in the other comments is to make sure you fully own the Chromebook. If it’s on loan from your school, or if it’s provided by your work, then you may be bound by some acceptable use agreement and therefore not allowed to modify the OS.