The Firefox print to pdf document produced is not exactly 100% compliant with the PDF specification, but still readable.
But the actual problem was the version of Adobe the person was using to view the pdf. Adobe has addressed the issue.
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.
Solution: Update Adobe Reader.