I recently had to re-install my PC and I decided to take the opportunity to freshen up my Firefox profile by abandoning my prefs.js file and only migrating settings and extensions as needed.
As part of this,I ran into an issue I dealt with a while back and had to look up once more.
http://ffextensionguru.wordpress.com/2006/10/22/firefox-20-close-tab-buttons/
I don’t like having my little red X to close the tabs actually in the tab. I like it at the end of the tab-bar. Just a quick rundown of how to change this:
Browse to about:config and filter for browser.tabs.closeButtons. Set that value to 3.