I have my tab settings on "Layers Only" and "Always Open in Current." The problem with this is that now when I open a new tab it opens them downloading and displaying the previous layer's website. This can be a insufficient use of bandwidth for those who want to browse quickly.
You might have had the URL Bar text highlighted at the time in which case the new layer button served as a duplicate layer button. The button recognizes selected text. If any text is highlighted/selected on the page or in the URL Bar, the button will open that text in a new layer, so it serves as a "Go to URL /Open As Hyperlink in new layer" button. If Keyword Autosearch is enabled via Tools, that selected text will be searched for in a new layer if it's not a URL. The Go button also recognizes selected text. These features were mentioned in the Read Me file of the betas but the RC1 Read Me is more basic. Documentation will be updated for the final.