Even for loading stuff under the file:// scheme on Chromium-based browsers, there’s a “hack” for it: 
It may seem my main browser is FF-based; but actually I mainly use SlimJet, which is Chromium-based, w/ the “–allow-file-access-from-files” flag enabled in its shortcut. 
However, since when p5js started to convert some of its loading API to rely on the Fetch API, that flag “hack” stopped working on them; for example loadTable(). 
The Chrome devs made the Fetch API to reject the file:// scheme on purpose! 
Of course the Fetch API works on FF under the file:// scheme just like anything else! 
The FF quick & dirty “solution” is given as the simplest & easiest 1. 
I don’t see how temporarily running JS scripts under the file:// scheme would impair n1 to deploy them under the https:// scheme later. 