[Fontconfig] Firefox & Typeface Selection

[Jorge Fábregas]

Hi everyone,

I'm on Fedora 20 using Firefox and, with the recent Wikipedia style
changes (they changed the site's typefaces), I started wondering what
actual fonts were being rendered on my browser.

Their new CSS font-family property is:
"Helvetica Neue", Helvetica, Arial, sans-serif;

If I use fc-match against these I get:

$ fc-match "Helvetica Nueue"
DejaVuSans.ttf: "DejaVu Sans" "Book"

$ fc-match "Helvetica"
n019003l.pfb: "Nimbus Sans L" "Regular"

$ fc-match "Arial"
LiberationSans-Regular.ttf: "Liberation Sans" "Regular"

$ fc-match "sans-serif"
DejaVuSans.ttf: "DejaVu Sans" "Book"

When I go to Wikipedia, the actual font being rendered is "Nimbus Sans
L" (confirmed by various Firefox addons I have).  This is the 2nd option
in the CSS property (Helvetica).

My question is:  Since I don't have any of these typefaces, why is the
2nd option being selected & not the 1st one (Helvetica Nueue)?  Is there
some notion of "preference" in fontconfig? Or is it a Firefox issue?
That is,  Firefox decided to use the 2nd option and asked fontconfig for it?

I don't really want to change the font being rendered. I just want to
learn what goes on :)

Thanks,
Jorge