If any graphic visual problem occurs during opening PDF catalogue directly from internet by clicking a flag (it happens e.g in Mozilla), you may avoid this problem by saving PDF on your disc and opening it later (after) from your computer disc.

So do it as:

1) on a flag click right mouse button

2) select " download-save PDF on to a disc",

3) start downloading a PDF file to your computer disc,

4) open this PDF file directly from your computer.