I have all my stuff- url bar, tabs, buttons, close/min/max, etc- on ONE bar. This extension fixed my screen space for buttons problem. However, like one of the other commentors, the popup behavior of this addon drove me nuts. I continued using it because I had to in order to free space for my tabs.
I had enough, so I decided to see if I could fix it. A dirty fix, but it works. Download the extension and use a decompressor to unpack it (rename it to a zip if necessary- thats basically what it is). In the result, go to: chrome/content/overlay.js.
Search for the onMouseOver method. Change it from what it is to::
Im using the // to make it more clear, though you can comment out code in other ways with java. Anyways, save the file and go back to the original directory. Now repack into something like: buttonizer-0.2-fixed.zip
After you do that, rename from buttonizer-0.2-fixed.zip to buttonizer-0.2-fixed.xpi and install it into firefox from the gear icon at the top of the addons manager. I would have just posted a fix, but its a really bad idea to install software from strangers you dont know. Its better if you do it yourself!
With this "fix", the toolbar will not popup at all when you hover over it. You left click, it opens. You click somewhere else (on the button or on firefox), it closes. Unfortunately, it doesnt close after you click on something in the toolbar. Ill see if I can mess with the method later and post a fix for that. Hopefully the dev will update this great extension..