As with other platforms, the update is planned in a two phase approach.
For Firefox 3.7, plans include combining the stop and reload buttons as their function is mutually exclusive; move the home button to the tab bar, and add a progress bar to each tab instead of the throbber currently features in all platforms. Unlike Windows, however, the menu bar is kept still. Also from other platforms, the keyhole shape for the back and forward icons is in. For cleaner looks, the toolbar separator are also gone.
Firefox 4.0 goes further, following the same patterns in other platforms: the tab bar would be at the top of the UI, and the menu bar removed with most of its commands moved to new Page and Tools buttons. A Bookmarks button would also be added to display all bookmarks.