safari won't open pdf in browser

Recently, something has changed with Safari. It no longer allows me to open all pages. This is particularly happening when I'm on a site that tries to show me a .pdf (like a bank statement or a journal article). A blank page appears as if there is nothing to display.

I really hate having to swap between browsers and would like to be able to stay within Safari; however, lately I've had to use alternative browsers. This problem does not exist when I switch to Firefox - there I am able to view the items that Safari won't display. However, it's difficult to anticipate which websites will function and which won't, so I end up having to try Safari and then, once I experience this problem, switching to Firefox to accomplish what I need. This is highly inefficient. I never had problems like this before "upgrading" to El Capitan. I regret ever making that change, but I cannot pinpoint that El Capitan is the source of this particular problem.

I'm using Safari version 10.0.1 on a MacBook Air with Os X El Capitan version 10.11.6. I've checked the plug-ins. The plugins for Adobe Flash Player, Adobe Reader, Java, Sharepoint Browser Plugin, and Silverlight are all set to "on" to allow them to function.

How do I resolve the problem so that the Safari browser actually functions properly?