I've been running firefox for this throughout development and just tested on another machine. Could be a network issue of some sorts where it's blocking a file from being downloaded? Alternatively it might be that you're on a version of firefox that this doesn't want to work on
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The game designer has confirmed it works in Firefox. If you're having a problem with hundreds of games that work for everyone else, the problem is not with the games. It's you.
Use Chrome, or stop using Linux, or go make games yourself. Just stop complaining constantly on every game page as if the entire world needs to cater to your exact whims.