Opera 12 forced everything into a new tab. Chromium-based browsers like Opera 36 allow links that are explicitly targeted for a new window to still be opened in a new window.
Holding down CTRL when you left-click the link might force some links into a new tab. Might not work with links in flash objects though.
You also might want to try this extension: https://chrome.google.com/webstore/detail/one-window/papnlnnbddhckngcblfljaelgceffobn.
You'll need this extension first to be able to install Chrome extensions in Opera.