I figured this out. The bookmarks pop-up that appears when I click the star at the top right (on an iPad) has a "back" arrow at the top left. I was inside the "Bookmarks Menu" folder; going back allowed me to see "Bookmarks Toolbar" folder. I wasn't expecting to see anything further up the "tree", but going back one more time reveals "Desktop Bookmarks" and a bookmark I added a few hours earlier, which also appeared on the start page under "Recently Saved" and (after sync) in the "Mobile Bookmarks" folder on my Mac. This doesn't seem like the easiest way to manage bookmarks, but at least I know that all my bookmarks are there.