This is what it usually means when something is "Chrome-only" - developers like me usually try to stick to standards, but don't have the time or resources to do

This is what it usually means when something is "Chrome-only" - developers like me usually try to stick to standards, but don't have the time or resources to do thorough testing of more than one browser. If it works on Firefox, that's gravy (and my current project does, from a cursory check), but I can't guarantee it in the same way that I can for Chrome. i.e. this particular dev probably tried it on Firefox/Linux, or got bug reports, and just decided to put up a disclaimer.