These days browsers are shipping with a their own PDF viewing software so you don’t have to install a third-party plugin. Firefox uses PDF.js, Chrome and Opera includes their own PDF plugin, Safari uses Preview and Microsoft’s new browser, Edge, even ships with a document reader. This is great in theory, but in practice it causes problems. Why? Because building software that correctly renders PDFs is hard (just take a look at the latest PDF specification and tell us it doesn’t give you a headache). And if that’s not a compelling enough reason, check Firefox’s PDF.js current open issues.
If you notice your generated PDF displays incorrectly in your browser’s viewer, the best option is to save any PDF documents to your computer and open them with Adobe Reader.