This isn’t a Hifi specific “protocol”.
“hifi://” links are a URI, infact all :// type links are, URL’s (http/https etc) are URI’s designated for “the web”.
If chrome is doing this then one of 2 things is happening. Either the uri is not properly “registered” on your system. Or chrome is being rubbish and breaking how URI’s are supposed to work. However if other browsers are working then most likley chrome is pulling something silly. Its possible there is a setting that turns on and off URI usage, as it could theoretically in some cases be abused.
An example would be somehting like this steam://run/390540, going to that link if your machine has the steam URI enabled and you have HiFi on steam, should cause steam to start trying to run it. However I believe discorse (the forum software used here) blocks URI’s that arent allowed (So you will have to copy it and paste it into your browsers address manually.)