The standard settings in web browsers is to block information from being opened in a new window, so called pop-up windows. If for example the integration with a logistics partner opens the package slip in a new window the web browser would by default block that window and you would need to change the settings to allow pop-ups from that website or completely.
When the browser blocks a pop-up window it usually announces it by showing an image at the end of the address bar.
When Firefox has blocked a window it usually shows it in two different ways. In the picture below you can see 1. an image at the end of the address bar and 2. a yellow bar at the top of the window. By clicking any of them you get the options to allow pop-ups for the website.
Firefox's own instructions about pop-ups
When Chrome blocks a window it announces it by showing an image at the end of the address bar. In this picture below you can see an example in the red circle. By clicking the image you get to the options for allowing pop-ups from the website.
Chrome's own instructions on pop-ups
Managing the pop-up windows in Safari is a bit more limited than the more common browsers. It doesn't, as in Firefox and Chrome, announce anything when it has blocked a pop-up. As in the below picture there is a setting where you can allow all pop-ups. The Safari settings can be found in the top left corner under the Safari menu.
Guidance on the subject: https://discussions.apple.com/thread/4271925?start=0&tstart=0