thanks for the report, checking this out now
edit: this is related to a WebGL issue in firefox which will hopefully be resolved with v85.0 https://hg.mozilla.org/mozilla-central/rev/3a105387c502
the game has a workaround for this FF issue in windows but it looks like the linux version is more aggressively optimized, which breaks the workaround. i'll look into alternatives
edit2: can you confirm that this version works for you? https://d2n726ceml0hx8.cloudfront.net/5224550/