Lets say you have five test cases and you want to execute all five test cases in same browser instance. When we say same browser instance it means open browser, execute all selected test cases and close the browser.
In order to accomplish this, go to BeatBlip agent > Settings > Create new session for each iteration and make sure this checkbox is unchecked.
This will execute all selected test cases in same browser instance.
In order to make this setting as default you have to save this selection on the web application in your project.
Open BeatBlip web application, select your project and go to Settings > Project Settings > Test Environment > test_adapter_reset_per_iteration and mark this setting as No.