When I updated to 3.5, the normal open a new tab button became a small vertical sliver that would appear only when you hovered on it to the right of the last tab. Now it's a + sign that does the same thing. I haven't installed or uninstalled any themes so I'm not sure what happened. Am I imagining this?

This is by design. All the other browsers now have the "new tab" button as a plus button on the tab bar, and since this has become somewhat of an informal standard, Firefox has followed suit in 3.5.

Edit: not sure about the "appear only when hovered" part, though. The button should be ever-present...

Just noticed that one of my themes wasn't there, so I reinstalled it. I like not having the open tab button taking up so much space, plus it doesn't pop up unless you are pointing right at it.

Phoenity Reborn

https://addons.mozilla.org/en-US/firefox/addon/7379