Ctrl-click on Firefox stopped working

Until recently (I noticed this today), ctrl-click has allowed opening a story in a new background tab on Firefox. This has stopped working. Instead, ctrl-click now behaves the same as regular click: opens the story in a new tab and switches to that tab.

Middle-click, and “Open in new tab” in the native context menu still open the story in a new background tab, so I think this must be the Newsblur website stealing the ctrl-click, and doing its own thing to open the new tab and the story in it. This is very inconvenient, since both middle-click and opening the link through context menu are cumbersome on a laptop.