When view PDF documents from the web inside Adobe, there are places where it shows double prints, if i open the same document using another explorer it fine

We have a web based program, that when i view a PDF document in firefox, it shows double prints of random letters. however if i use internet explorer the document views fine. If i try to print the document in firefox it will print the Double prints, but if i print it through internet explorer the document is fine. please advise as to what the problem could be.