Sure.
Hi again,
As much as I want to, I just wasn't able to recreate the bug you're facing - tried both on my Linux box(arch btw) and on my steam deck - no issue on Firefox whatsoever.
While I can't hold you hostage in debugging this for me, what I did was I uploaded downloadable builds for both Win and Linux. The Linux build I've tested both as just running the executable and adding in steam as a non-steam game. I realize this may put you and other people off(myself included, not really into running random executables from the internet), but that's honestly what I can do for now.
Worth saying: the Deck runs(if I'm not terribly mistaken) the same GPU family and driver stack as your 6500 XT, so not reproducing there is a bit more meaningful than "works on my machine"; it makes me suspect something recent in Mesa rather than your card. You're on 26.1.6, which is well ahead of what SteamOS ships, so might be worth a retry after your next Mesa update.
Also: the Linux download may need a chmod +x before it'll run;
last but not least, even if you don't end up trying the game - many thanks for the provided feedback, it's all been very useful to me
Huh, I wonder why my system in particular seems to be cursed. Sometimes I wonder if I should even keep reporting these crashes as most of the time it seems the dev can't replicate them and I end up throwing them into an endless pit for no reason. But it does run with the Linux executable, so I can provide proper feedback now.
Here's a snapshot of my first run stats, without looking at any part of the description, and only knowing the genre:

1. About 6 minutes, though I've never been particularly skilled in these games. A projectile from a cultist took my final 4 hp.
2. Like old single-tower defence games, but you can move, and upgrades are random. I couldn't say the premise is particularly outstanding compared to competitors in the modern 'Survivors-like' genre, but it seems playable enough for a casual project.
3. Health goes down when something hits you. Sanity goes down when you're near the enemy or when ??? Not sure why it continued to go down - maybe related to one of the cards I took that said something about sight, but it wasn't clear what that meant.
Glad it runs, and that's a genuinely useful writeup, thank you.
On the reporting thing, since you mention it: your crash report is the reason there are downloads on the page at all. There were none before you posted, my initial take was browser build or nothing. So it didn't go into a pit. It's why you were able to check it out tonight, and why the next person whose browser chokes has somewhere to go instead of a stack trace. Worth knowing before you decide the reports aren't landing anywhere. For what it's worth, I have a similar experience in reporting bugs/issues - and if my opinion matters to you - keep doing it as long as it doesn't cost you too much energy.
You're right about the card, too. The Third Eye cuts your maximum sanity rather than draining it, and nothing on screen tells you which of those just happened - the bar gets shorter and you reasonably assume something's eating it. That's the second time a card's wording has made a mechanic look broken, so it's going on the list as a pattern rather than a one-off.
The blunt read on the premise is more useful than a polite one would have been, so thanks for that as well.
Six minutes with a cultist finishing you off is around the middle of what I've seen, for whatever that's worth, you're not the outlier you think you are.