While Firefox 4 is still in beta and even though it seems it will be released in March, it might actually be further delayed, the first Firefox 5 mockups are already starting to emerge.
It seems that Mozilla will adopt something called "site-specific" browsers (this is basically the old Prism with a new look) or "desktop apps" starting with Firefox 5, which will have an integrated site menu. Here are some mockups to understand how that will work:
These are just the initial mockups so things might change. Also, we'll probably see a lot more changes in Firefox 5 as well as 6 and 7 - because Mozilla is planning to release all of these next year.
For more mockups, see:
[via Bitelia & ConceivablyTech]