Just upgraded to Firefox 3.6 and I am a little annoyed by the new "feature" of tabs opening next to the tab where you open the new tab from. While this might be convenient to some people, I got used to the "old" way of handling tabs and find myself constantly wondering where this new tab is. I might give it a few more days to see whether I get used to it but in case you are annoyed by that too and want to "fix" this here is how you can disable the new “Insert Related Tab After Current” tweak in Firefox 3.6.
This will convert Firefox back to opening a new tab from a web page on the far right of the tab bar, rather than right next to the tab you opened it from.
If you decide that you actually like it and want to switch back, follow these same steps and toggle the “false” back to “true”.