User-Agent: Mozilla/5.0 (X11; U; Linux i586; en-US; rv:1.2b) Gecko/20021018 Build Identifier: Mozilla/5.0 (X11; U; Linux i586; en-US; rv:1.2b) Gecko/20021018 The default font used by the Mozilla UI (and anything else that doesn't override it, including web pages themselves). Reproducible: Always Steps to Reproduce: I did a quick grep through all the CSS files in the Mozilla installation, and the only instances of "font-style: normal" I found were for a few specific HTML & MathML elements and a couple of UI components. My theory is that whatever it is that everything inherits its style from doesn't actually specify a font-style, so everything is in italics by virtue of the fact that no font-style preference was listed and Xft2/fontconfig happened to return italic fonts before non-italics.

Sounds like a dupe of bug #175025

I don't think so. It's the right font family, but the italic face instead of normal.

*** This bug has been marked as a duplicate of 175025 ***

This is cause by a bug in Xft/FontConfig. Basically, it doesn't deal well with fonts that have styles other than "Regular", "Bold", "Italic" or "Bold Italic", while I have fonts (including the UI font) with styles like "Narrow", "Oblique" and "Black." When a request is made for a font in a family with "odd" styles, the returned font is basically a random font from that family. I verified this by temporarily uninstalling all my "odd" Helvetica fonts, and then restarting Mozilla. Without the "odd" fonts, the UI font is normal.