http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/gfx/thebes/src/gfxFontconfigUtils.cpp&rev=1.5&mark=419-426,449#419 When a group of fonts have a common family name, but differing lists of family names, this assertion fires. (A font can have more than one family name.) e.g. (gdb) p fs->nfont $14 = 3 (gdb) p FcPatternPrint(fs->fonts[0]) Pattern has 1 elts (size 16) family: "Arial"(s) "Arial Narrow"(s) $16 = 10 (gdb) p FcPatternPrint(fs->fonts[1]) Pattern has 1 elts (size 16) family: "Arial"(s) "Arial Black"(s) $17 = 10 (gdb) p FcPatternPrint(fs->fonts[2]) Pattern has 1 elts (size 16) family: "Arial"(s) $18 = 10 I think the assertion can just be removed, as the code is successfully detecting that we have at least one match (and the specific match out of the three can be determined later).

I think that IsExistingFont should return 1 at that time. Because, when the name is cached, we cannot return the actual count.

Returning 1 seems consistent.

checked-in, thanks!