Hi ACCA Game Page. I understand your concerns, but even Thor himself promotes mainly the Steam platform on which we would also like to release one day. Almost every game on Steam is desktop and played fullscreen. Only this year Thor changed the rules that games need to be playable on the web because of malicious content/files/viruses. We weren't even focused on small screens because we are not interested on mobile platforms at all.
1. this can be solved by multiple choices. Either you have a big 4k+ monitor and you can create separate desktop for each "corridor" (corner) of the monitor, then the fullscreen is played only on one corridor. Or you can have multiple monitors which solves this. How are you solving this problem when you are actually playing a desktop game?
2. as a senior web developer - yes your tab can crash, but because browsers are nowadays multithreaded it's not actually touching any of the other tabs you are working in.
3. If this was a game you would actually payed I would personally fix this in a day. But this is free content created by no experienced game developers at all, learning and having fun together, working many hard hours even when some of us are on vacation with our families and children.
4. The fullscreen is a choice that you actually are allowing on the itch side, not unity. You don't need to click it at all.
5. If you have 1-2GB of RAM then I understand your concerns and I would use a different browser which is more RAM-friendly and not Chrome-based browsers.