I'm assuming the more browsers you can support the better.. But is it okay to ignore Internet Explorer? :p I'll be trying to support Edge because that now has the Web Audio API, along with Chrome, Firefox and *maybe* desktop Safari if it just magically works out of the box.

Am curious about how much weighting browser compatibility will have, especially as most WebGL exports seem to ignore Internet Explorer too?

Chrome or Firefox should be fine... it really depends on individual judges. Personally, i might have a look at the game in IE/Edge, but mostly will be judging in Chrome and Firefox.