If this were a commercial project then I could understand the complaint.. but this is just a small, for-fun project and they have little motivation to put the extra effort into support for all browsers.
Bellard (yes, him) already had a working VM of Windows 2000 in the browser around a decade ago, with no specific "support for all browsers" (whatever that means):
Also, look at 8086tiny, or PCulator/XTulator. These could be ported with ease to EMSCripten and run everywhere, not just in Chrome.
Chrome almost became the new IE and Google, despite it's motto, the new Microsoft. Ok, the desktop? Android rules the smartphone sales in the world, and its online services are used by millions, with far more metadata grabbing than w9x/wxp on its day and with the same propietary OSes.
Consider: maybe it's not a matter of non-standard APIs, but bad performance. It's not simply porting to the lowest common denominator, it's making sure the code doesn't run at a snail's pace because the JIT/wasm compiler has a pathological edge case.
I'm not really complaining; just harking back to a shitty time that is, on some commercial sites, threatening to return. Especially as Apple finally allows Chrome on iOS, eroding the main bastion against it: Safari.
