The Linux version of Firefox 4 is slightly different to the other versions. Menu options especially. As you read below, there were some differences in layout between Firefox 3 and 4, and some things I cared about and changed, and some things I didn't care enough to fuss about them.
I changed the main button bar using View -> Toolbars - Customize.
I removed the Google search box. I already found that I could type my search terms into the regular URL box and a Google search would be done. So I simplified the bar by removing the redundant Search box.
The Reload and Stop buttons appeared on the far right, outside the URL box, so I dragged them into place over on the left beside the Back and Forward buttons. And I dragged the Home button over there too. That's what I am used to, that's what I like. I've used them in the URL box for a few days just to see if it was an improvement, and it wasn't and I did not like them there, so I am happy to move them back.
I would still like the status bar on the bottom back, but so far that's only available with an add-on. I'll leave it alone for the time being, in the hope that they bring back the status bar without needing an add-on. I can still access Firebug by turning on and off the Add-On bar with Ctrl-/.
One gripe I have is the terminology. You can download an add-on, but once it's downloaded and installed, it's called an extension. I've been irritated about this difference for years. Call them all add-ons or call them all extensions, but don't call them by both names. Some instructions refer to add-on, some refer to extension, and this can be confusing. Mozilla people - aim for consistency.