Safari's "Preview" and "Download" button icons not working
When reading a pdf file downloaded fresh from the internet in Safari, the "Preview" and "Download" button icons that magically appear at the bottom of the pdf file inside the Safari window no longer do anything; i.e. I can click on them, they change colour showing the click was accepted but they neither download the material to my selected download folder nor open Preview. The + and - zoom buttons work however and the keyboard shortcut command-s also works correctly. If I use Safari to open a pdf that has already been saved on my HD, i.e. by dragging it into Safari's address bar or control-clicking the file and selecting "Open in Safari", then and only then do the "Preview" and "Download" buttons icons work...
Apart from downloading and reinstalling the entire MacOS, would anyone know how to fix this bug? Many thanks in advance.
David
[MacOS 10.9.4 running the latest version of Safari (7.0.6)]
OS X Mavericks (10.9.4), Safari 7.0.6