The default xp theme includes a nifty unified back/foward/history button that I like. If you like it and miss it there is a way to get it under linux.
Copy the clasic.jar from a windows FF3 install. It’s located in FF3 chrome folder.
Note :You might want to backup the linux originals first.
Then place it in your ‘/usr/lib/firefox-3.0/chrome/’ directiory in ubuntu. Remember to restart FireFox.
If you don’t have access to a windows box download here