Ah! So it is a font issue …
The font should be Verdana, but my Safari version uses Geneva instead (from the font stack in the CSS file). I have Verdana installed and activated … but Safari doesn’t use it.
So that’s why we have this difference …
Newer versions of Safari don’t like certain “system fonts” because they are deemed “unsafe” (because of tracking) … Duncan wrote about this some time ago in this thread: