Sorry to say but I wont be able to fix this. Its based on a really old version of godot that I really dont want to go back to at this point and the game isnt even that good.
Also the first time I heard of vivaldi browser lmao.
I didn't expect you to be able to fix this, especially since it seems to be a problem way out of your control if it crashes the whole browser.
It's very fair not to know about the Vivaldi browser, but since it's based on Chromium I just tried it in a clean (w/o plugins) version of Chrome and could reproduce it there! I guess this is just yet another thing to watch out for when releasing Godot games in the web, FYI. :'D