@MJLew OK, I found the hidden interface element (see the rant below) that Phaedrux mentioned, but even though it promises when the command key is down to open the link "in a new tab behind the current one" is does no such thing. It just scrolls the current tab to put the selected command at the top.
When I hold the control key down I can get the popup that Infiniteloop showed (and it works), that is not how I have to use proper links in the browser.
<rant> Hidden interface elements seem to be all the rage (even with Apple software) but they are terrible things for core elements of human computer interface. People should not have to hunt around for random hotspots that do surprising things, and people should not have to RTFM to work a web-page!