Photos: Firefox 4 team try out new user interface
Typing in a web address in Firefox 4.0 - How Firefox 4.0 may look
When you type in a URL, the address bar "go" arrow turns green.
Do you prefer browser tabs above or below the address bar? Software developers at Mozilla Foundation are trying both.
They are also looking at how to give users more feedback on what the browser is doing when the user types in a URL to go to a website.
These sceen shots show what the Firefox developers are looking at for version 4.0.