IDEs launch a browser when you run the web application. You can instruct IDE to launch the browser that you prefer. Your system default browser might be Chrome and you might want you're development done with Firefox because of it's simplicity to identify/debut the HTML elements and Javscript issues.
I'm going to explain how we could modify the default browser with JDeveloper IDE
1. Choose "Prefereces" from "Tools" menu.
2. JDeveloper will open preferences dialog box. Choose "Web browser & proxy" from the left as displayed below
3. Enter the browser absolute path you would prefer to open while running web applications. You can specify the proxy settings as well