I love tabs and use them heavily, but I wish they behaved on the desktop like they do in Chrome on Android, where hitting the back button when there's no prior history closes the tab. Sometimes I open a link in the same tab (plain old forward navigation), sometimes in a new tab. I then need to remember that the first one requires a back button when I'm done, while the second requires a Ctrl-W. If I forget and use Ctrl-W when I should have used the back button, then I lose my history (and have to go to the "Recently Closed Tabs" menu to restore it).