Fonts from local Mathjax fail to load in Firefox 68

Created by: zoquda

Issue Summary

The docs explain that if you are viewing a page in Firefox through a file:/// URI, locally stored MathJax fonts can be used as long as they are located in either the same directory or a downstream directory. This approach seems to work in Firefox 67 (and lower).

However apparently in Firefox 68 a change was made to the same-origin security policy, resulting in access to the local MathJax font files being blocked regardless (which in turn causes equations to fail rendering).

Steps to Reproduce

Download this fork of the MathJax repository (the only change is that HTML test files have been moved up in the directory tree).
Open ./index.html in Firefox 68 (i.e. access the HTML file using a file:/// URI).

Subsequently the equation in the displayed HTML page fails to render in HTML-CSS. On the page the following message is shown:

WARNING: MathJax's web fonts don't seem to be available.

Furthermore in the Firefox console the following message is displayed:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at file:///C:/Projects/MathJax/MathJax/fonts/HTML-CSS/TeX/woff/MathJax_Size1-Regular.woff?V=2.7.5. (Reason: CORS request not HTTP).

Technical details:

MathJax Version: 2.7.5
Client OS: Windows 10 (version 1809, build 17763.615)
Browser: Firefox Quantum 68.0.1 (64-bit)