As of Sparkle 2.8, you will be forced to replace most system fonts you might have been using to either a “safe” system font, or to a web font.
Sparkle is now enforcing the use of web fonts for fonts that would not work in Safari.
Why would some system fonts not work?
Last year Apple found that ad networks were using the list of system fonts installed on your Mac as a way to track you, even in private browsing mode.
The tracking code detects the different fonts installed, scanning through a list of 500 font names to see which your browser can load. Since everybody has different fonts coming from different places (Adobe, Microsoft, other software or sites), your Mac’s list of installed fonts would be unique and make you unique and trackable.
To solve this the Safari “Intelligent Tracking Prevention” feature only allows a couple dozen well known system fonts to work (Helvetica, Times and the like).
With Intelligent Tracking Prevention, everybody’s Mac looks the same, same list of fonts, so tracking is thwarted.
This feature was released along with Mojave but also deployed to High Sierra’s Safari.
What this means is any system font you might be using that’s not in the list, won’t work in Safari (Mac or iOS).
Truth to be told, the font wasn’t working anyway if it wasn’t installed on the visitor’s browser, and while there might be limited occasions where this is the case, in general it’s best to use web fonts that work across all browsers.
So how do you get your website working again?
One option is to install the system font as a web font in Sparkle. For example, using a system font might have been an accident. Perhaps you found a font on fontsquirrel.com and installed it locally on your Mac. All of those fonts can be loaded in Sparkle’s custom web font pane, and used as web fonts. Quick and easy.
Otherwise, if the font you were using is a commercial font, and if you have a license for use as web font you can proceed to install it as a custom web font. This is often not the case.
Unless you have a very specific taste for a font, you can frequently find free alternatives to commercial fonts. They’re usually a Google search away, and perhaps already available in Sparkle’s font panel.