Thanks for the replies. I am using SAP WebIDE to write UI5 apps, and when I run the preview, it opens a new window to load the app. I have already disabled the popup blocker for this URL. When the site loads, it prompts for a login, which is just a standard HTML prompt requesting username and password. I start typing in my username and password, but before I can complete, the login prompt box goes away. I was able to get around that by copy/pasting my password in (quicker than typing) and selecting 'save password' when prompted. The login request is actually coming form the backend; when the app requests data, it needs my network/user credentials.