A impressão do Firefox para o documento PDF produzido não é exatamente 100% compatível com a especificação PDF, mas ainda legível.
Mas o problema real era a versão do Adobe que a pessoa estava usando para visualizar o pdf. A Adobe resolveu o problema.
PDF documents that contain Type 3 fonts with missing operators are non-compliant with the PDF specification. These non-compliant PDF documents are typically generated by third party products. When trying to opening the document, users see an error message, "Cannot extract the embedded font 'F0'. Some characters may not be displayed or printed correctly." PDF documents open correctly in Reader/Acrobat 7.x, but not 8.0 or 8.1. The root cause is Type 3 fonts that do not comply with the PDF specification, which requires either the 'd0' or 'd1' operator in every Type 3 character procedure. In version 7.x, if the offending character was not displayed, the PDF document opened normally. Version 8.0 catches this error even if the character is not displayed. The updated behavior will ignore the missing operator when the character procedure is empty.
Solução: atualize o Adobe Reader.