There is a PDF feature, which are called "layers". I see this as an advantage, that Firefox supports those, and also supports enabling / disabling (set visibility) them when a PDF file is opened in the browser itself.
However, when someone want to print this file (with some layers enabled and some disabled), it would always print everything (all layers enabled / set to visible), therefore it would be good, if the current layer settings would be also applied when someone prints the document.