The Web Inspector @font-face previews should be editable to allow previewing arbitrary content. We could also have a popup that let you pick other stock content, like symbols, accented characters, etc.
I have no idea what feature is described here. Please re-open if it still makes sense as an enhancement.
We show a font preview content view for downloaded fonts. That preview just has A-Z:a-z:0-9. Making it editable so you can try other characters in the font would be useful.
Like so: http://timothy.hatcher.name/font-preview.html