You can rearrange a lot of the buttons using the Customize feature. Please see: Customize Firefox controls, buttons and toolbars.

• There are "flexible spacers" on the left and right of the address bar that you can remove in the Customize pane to remove the centering.
• There is a Themes button at the bottom of the Customize tab to modify the background color(s) of the toolbar area.

I realize the squared off tab shape is polarizing; that can be modified using custom style rules, but it's a bigger project.

What other issues need to be addressed?

I hate it too, especially the new tabs page.

Ihatenewfirefox said

I hate it too, especially the new tabs page.

I guessed that from your username.

To switch off the "Activity Stream" new tab page and show the old layout:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste newt and pause while the list is filtered

(3) Double-click the browser.newtabpage.activity-stream.enabled preference to switch the value from false to true

Whoops, that was backwards, change the value from true to false to disable it.