I have been using version 4.01 of Firefox on two different machines now for about 2 days. Just be aware of a few things:
Right-click on the toolbar area and you can turn on or off the menu bar. You will also find an item in this right-click menu to put the tabs either at the top or at the bottom of the tools area.
As you found, the Norton Toolbar works in Firefox 3.6.16 and 3.6.17, but if you want to be sure that the Norton Toolbar is available in version 4.01 of Firefox, then you need Norton Internet Security 2011 or Norton 360 Version 5. You can find several discussions about this in the Norton Community Forum
The bookmark system in Firefox is not at all as easy to handle as the favorites system in Internet Explorer. In IE, much easier to use and understand.