Is it possible to start the browser with a given URL by simply pressing a pushbutton?

The simplest way is to introduce an image that looks like a pushbutton with, for example:

Image   (12,60) "url_button.gif"   Start=""
The URL can include &[..]-variables.

Alternatively, with InputAssistant, createa  pushbutton which starts an InputScript and in the InputScript use the "Start" command with the given URL, e.g.

Start ""