There's probably no general problem with the computer that can cause both Chrome's and Firefox's problems at once.
There are, many.
video card drivers up to date ?
Latest versions of the browsers ?
Disabled all unneeded browser plugins ?
Cleared cache and or temporary files ?
Did you run them firefox and chrome in paralel with windows ? or installed the macos versions ?
Did your IT class firefox run the game normally ? (if it had it and you tried that)
Those are some approaches you could check.
Generally, Chrome is considered top notch to test and run the web variant games of construct 2 in.
Derrived from your statements, I would say the culprit is your local system. Seeing as the game even ran fine on an internet explorer on your school.