Quote:
They [...] changed that little X that I use all the time to close tabs. Small issues, to be sure, but annoying.

Type about:config in the address bar. Change browser.tabs.closeButtons to the value you want:
  • 0 - Display close button only on the active tab
  • 1 - Display close buttons on every tabs
  • 2 - Never display close buttons
  • 3 - Display single close button at the end of the tab strip (The way it used to be)
Personally, I use Ctrl-F4.