Luckily there's a 'fix' for it.
Type about:config into the address bar & go to > Browser. tabs.closeButtons
This preference controls how close buttons can be displayed on tabs.
0: Display a close button on the active tab only
1: (default) Display a close button on each tab
2: Don't display any close buttons
3: Display a single close button at the end of the tab bar (Firefox 1.x behavior)
