If I right click a folder of bookmarks and select "Open All Bookmarks", the focused tab switches to the first bookmark in that folder, despite the fact that I do not have the following General preference item: "When you open a link, image or media in a new tab, switch to it immediately". While that item doesn't specifically describe the "Open All Bookmarks" situation, it's kind of the same idea. I have groups of bookmarks that I often visit, and I don't my focused tab switched every time request one. (related thread that discusses opening individual links as new tabs: https://support.mozilla.org/en-US/questions/1405016)