As of Firefox 2.0, when you open new tabs, each tab gets a close icon which can be clicked on even if you are in a different tab. In some ways this is convenient, but I'm now finding it to be a big pain the butt since I occasionally hit it when I am trying to go to the tab, not close it.

Luckily, the behavior of the close tabs is configurable. To adjust the behavior, type about:config into the address bar (the place where the URL is shown). Once you do this, you will presented with a very long list of preferences.

Scroll down to the preference called browser.tabs.closeButtons. The default value will set to 1. If you double-click the mouse on this line, it will bring up a dialog box that allows you to enter a new value. Valid values are 0-3, enter the one you like and the behavior will be changed. Here's what the values mean:

0 - Only show the close icon in the active tab (this is the one I like).

1 - Show close icons in all tabs (the default behavior).

2 - Don't show any close tabs.

3 - Show the close tab off to the right-hand side of the tab area. Clicking it closes the active tab. This was the behavior that Firefox had prior to Firefox 2.0.