Short answer: you can't.

Unless you have total control over the end-user's computer, it can't be done. As long as they can access it, be it to view or to print, they can copy it. You may be able to make it difficult or annoying to do so but it will always be possible.

Consider: To print the data, they have to copy it from memory to the printer. What would stop them from intercepting the data there, possibly even with specialized hardware? I know this is extreme and almost no one would do it but my point is that they could.

And there are many, many ways that are much easier whereby they could copy the data that you could not stop without standing over their shoulder as long as they view it (or longer).

If you (and your boss) would settle for merely making it difficult, then you should perhaps ask yourself: Why? Why are these people that you are allowing access to your precious data not trustworthy enough in your eyes that they would copy your data? Perhaps they should not be given access in the first place. Or perhaps you should not be so paranoid about people copying your data.

Of course, it's entirely possible that I'm just confused. ;-)

Addendum: If by "browser" you mean web browser, then even making it difficult is nigh unto impossible. They could always wget(1)... (Unless, of course, you're talking about Windoze Lusers... ;-)

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.