New tabs opening in the middle of the tab bar instead of at the end.
Opening a new tab from a link would open the tab right after / behind the tab you are currently viewing - not at the end. This makes for a very confusing / annoying / clustered browsing as it's impossible to keep track of what you opened (if you are opening more than one link from a certain page).
Operating system
WinXP
Opaite Mbohovái (1)
To revert this to the previous behaviour of all tabs opening at the end:
Enter about:config into the address bar, click through any warning, then into the Filter box paste:
browser.tabs.insertRelatedAfterCurrent
Double-click the line listing that preference to change the value to false