Firefox has provided a provision to resize this over sized button. Just navigate to ‘View’ – ‘Toolbar’ option, after launching Firefox 3. Click on ‘Customize’ button, check the box ‘Use small icons’ then click ‘Done’. That’s all.
In Firefox 3 the back button is large round shaped one. It causes the height of the tool bar to increase a little. Some of you may want to make it the same size as the forward button, just like most other popular browsers have.