You can setup Adobe Reader to open PDF files within Firefox instead a separate window. https://supp

You can setup Adobe Reader to open PDF files within Firefox instead a separate window.
https://support.mozilla.com/en-US/kb/Using+the+Adobe+Reader+plugin+with+Firefox

https://support.mozilla.com/en-US/kb/Opening+PDF+files+within+Firefox

If that doesn't solve the unreadable display, try Adobe support for help with that issue. http://forums.adobe.com/index.jspa