I created a report with Report Builder 3. My users are us to seeing reports displayed on screen with no page breaks. It looks like the default is to have page breaks. I found that in the report properties there are a couple of properties to manage page breaks.
In Report Builder, right click outside the report body and click Report Properties. In the properties window there is a page section when you have it sorted by property category. In that section there is a property called InterActiveSize. If you set the height and the width of this property both to be 0 the report is displayed on screen in one long page with no breaks.
The other property is PageSize. This has to do with the printed page. It is right below the margin property where you can control margins. I think this only controls them for the printed page.