I am not really good at Dutch, but now my money is on "Bladeren" or "Blader" (imperative). The meaning at that time could well have been "turn the page", like the German analogue, and as Jack (15 Jun 11 - 04:41 PM) guessed.

In current usage, the verb means either to browse at random, or to turn many pages to find something particular. Many other words have changed their meaning more radically.