I personally like being able to close each tab individually in Firefox but if you get too clicky happy you can close tabs by mistake which can be a pain. Here's a little trick to remove the x's from each tab which makes it impossible to close a tab in error again.
Type about:config in the address bar. You will see the message (if you're doing this for the first time) "I'll be careful I promise", click on it.
Scroll to brower.tabs.closeButtons, double click on it and in the Enter integer value box
Enter 0 = Firefox will display a close button only on the tab that you're currently on.
Enter 2 = Firefox will not display a close button on any tab
If you want to change it back just do the process over again and type 1 back in.
If you want to be able to close a tab while in this mode just right click on the tab and choose "close tab".
Philly
You can also right click on the tabs and hit "undo close tab" and that will bring your closed tab back to life!
Dancin' with myself...