One of the things i disliked about the Firefox 2.0 upgrade was the way it handled tabs.  For someone like me who routinely has 8-30 tabs per window, and 4-6 windows open at once, the Firefox 1.x method of having a single close button for all tabs in a fixed location means that closing multiple tabs in quick succession is much more efficient.  (More discussion can be found in this thread at the Mozilla forums site.) It turns out the behaviour is not gone completely, just not enabled by default and not visible in the preferences dialog.  To restore the Firefox 1.x method:

• open a new tab or window
• type about:config as the location
• type tabs in the filter field
• locate browser.tabs.closeButtons in the list
• double click it and change the value to 3

More information can be found at this Mozilla knowledge base article.