In Firefox 2.0, when you open more than one tab the tab bar appears under the address bar. Each tab should, by default, have its own red 'X' which you can use to close it. Alternatively, you can right-click each tab and select Close from the menu.
If you don't like tabs, you can simply omit using them altogether and open new links in their own windows. Just go Tools->Options->Tabs and select the option to load all sites in new windows instead of new tabs. You can also use an extension such as Menu Editor to hide the tabbing options from drop-down and right-click menus.
If you want to get rid of tabs completely in Firefox, though, you have to revert back to Firefox 18.104.22.168, currently maintained for those who wish not to use Firefox 2.0. You would, however, lose the other features offered under 2.0, including spellcheck and session saver. (You would need to install the third-party extensions to regain said functionality.)
In IE7 I disabled tabs. Can this be done in FF? If not, how do I close a tab without closing all of them?.....Maggie