this report has been filed here:
"for several days now evince displays PDF files generated by printing with firefox to cupspdf incorrectly. It renders embedded graphics as black boxes (example attached).
I still can print and display these files with okular correctly, so I guess it is a problem of evince. (I first opened a bug for ghostscript but then realized that my printer's queue and okular process it correctly.)" BTW acroread is not showing the graphics either but it works fine with xpdf. Thanks!.
The problem is cupspdf has turned the images into Type 3 fonts. The cairo output from poppler does not support Type 3 fonts with color images and it would not be easy to fix.
I'm not sure if the PDF standard allows Type 3 fonts with color images. The fact that acroread also fails to render the images in this file suggests this is either not permitted or a corner case that no one uses.
I suggest using the builtin PDF writing capability of firefox (print to file in the print dialog). It produces a smaller better quality PDF and unlike the cupspdf output the text can be copied and pasted from the PDF.