Comment 7 for bug 1333627

By the way, the file 30-metric-aliases.conf breaks font selection on all web pages containing font selectors like this:

font-family: helvetica, arial, sans-serif;

in the case where Helvetica is NOT installed, while Arial IS installed. In css the font names are prioritized, and if the first isn't installed, the second should be chosen, and so on. So the web page should display in Arial, instead it displays in Nimbus Sans L. Because when the browser requests helvetica from fontconfig it should be denied and try the next option (Arial), instead it gets Nimbus Sans L and never gets to test for Arial.

This problem exists in several browsers. I'm not sure whose responsibility this is, browser or fontconfig.