Annotations and highlighting from xournal++ are opaque only on this pdf viewer

I use a notetaking app called xournal++, which is helpful with graphic tablets. There is this issue that seems persistent, When I annotate anything via xournal++, I export it to pdf and view it on firefox, The highlighting which is supposed to be slightly transparent, Appears completely opaque, blocking text underneath it Now I Would normally contact the xournal team, but it seems this issue is only present in mozilla's pdf reader I have tried opening other pdfs, although the same results occur (Also apologies in advance I have no clue which category this should be in)