Firefox 4 may be getting tabs in title bar option
As with Google Chrome, your tabs will only move to the topmost area of the window when maximized. The feature has yet to be delivered to the Firefox 4 nightly builds, but you can download experimental versions from developer Bill Gianopoulos. Windows and Linux versions are available at the moment. Gianopoulos states "These builds are essentially the same as the corresponding Official Trunk Nightly Builds" but notes that his builds include "not yet landed fixes for some MathML issues, and User Interface changes planned for Firefox 4, as well as bugs that I am currently working on or find particularly annoying."