Please do the following:

1. Click Help | Restart with Add-ons disabled.
   
   
2. In the next menu which appears, checkmark: "Reset toolbars and Controls".
   
   
3. Finally, click the button called "Make changes and restart".

You have a couple of outdated plugins installed which expose your system to exploits. Update the following a.s.a.p.

• Java via http://www.java.com/en/
  
  
• Adobe Flash via http://get.adobe.com/flashplayer/
  

See: http://www.adobe.com/support/security/bulletins/apsb11-12.html

Make sure that you do not run Firefox in full screen mode (press F11 to toggle).
If you are in full screen mode then hover the mouse to the top to make the Navigation Toolbar and Tab bar appear.
You can click the Maximize button at the top right to leave full screen mode or right click empty space on a toolbar and use "Exit Full Screen Mode" or press F11.

See also;

• http://kb.mozillazine.org/Corrupt_localstore.rdf

I have the same issue: See the difference between this and this.

Whenever I start a new, maximized instance of the browser, and don't have any others open, the minimize/maximize/close buttons disappear and the whole top bar goes black (except for the orange Firefox button and the drop-down next to the three affected buttons).

I did precisely what Xircal specified, and the problem persists. The effect does go away after mousing over the bar, and as I said, only occurs in the first maximized instance to open. However, it recurs, and while it's clearly not dangerous I don't think it should be happening.

I do have similar issue when I resize the browser. In windows 7, we have a feature that draging the browser window to a side will resize it to half of the screen. Whenever I do this, minimize, restore and close buttons dissapears - however, they remain invisible. I can still close, resize or restore by clicking the places where they supposed to be by guessing. When I expand the size of the browser, those buttons start to appear (attached figure is such a situation). Please be kind enough to provide a solution.

You can try to minimize and restore the window to see if that helps.
You may have a problem with the display driver, so check if there is an update.

I have this problem too with a fresh install of Firefox 5 under Windows 7 on a brand new HP laptop. The minimize/maximize/close buttons are there until I maximize the window then they go black (exactly as the screenshots from Aexis).

I've solved my problem by uninstalling Stardock MyColors that came preloaded on my HP laptop. I think it may have been a conflict between that and my Radeon 5850 graphics card as it got much worse after updating the graphics card drivers.

Hope this helps someone, and perhaps one day computer manufacturers will stop installing unnecessary rubbish on their machines.