Okay, I just checked Chrome, and there is no way to override the website's font choice, except with an extension. You can specify a default font, though. This may be where jesse_the_k's suggestion would work, of having the website defer to the default font, but I don't know how to code that.

Of course, this would mean that, in Safari, the user would simply see Safari's choice of default font, with the user having no choice.

Incidentally, Safari and Chrome are by far the most popular browsers currently (at least, for sighted users; I don't know about visually impaired users).