Are you using Firefox 4 in Ubuntu? If so, you may not be too pleased with how the default theme looks. A quick visit to the Personas website can help you make Firefox blend in nicely with your system.
As you can see in the screenshot above, the personas theme makes the Tab Bar stand out nicely from the Navigation Bar instead of the two “blurring” together.
Note: We moved the tabs to the top and reduced the Firefox Menu to a toolbar button in our screenshot using the Compact Menu 2 add-on (link provided below).