The UPGRADES ENCYCLOPEDIA and ACHIEVEMENTS tabs can't be accessed on my computer which is running linux. The tabs light up when I hover the cursor over them, then stay lit when I move it away. Clicking on the tabs has no effect. The hero tab behaves normally though. I know this is likely a linux problem since it exists over different browsers and have had no problems with computers running windows. Has anyone else had this problem? Or know a solution?
As you've mentioned, it's almost certainly a Linux (or Linux-browser) issue, since there are no reports of this problem on Windows (or Mac, that I know of). Ruffle, the emulation tech being used to get Flash games to run, works in your browser... so it's not unusual for there to be edge cases with less common browsers.
Solutions: try using Chrome or Firefox? or Windows. Ruffle is always being updated, so a fix may come in the future.