Would be pretty idiotic to not close it, otherwise opening a bookmark would always require a second click to close the popup.
Anyways, you can go to about:config and set browser.bookmarks.openInTabClosesMenu to false - afterwards you can hold Ctrl (or just click the middle mouse button) while clicking a bookmark from such popup and the popup should stay open.
Would be pretty idiotic to not close it, otherwise opening a bookmark would always require a second click to close the popup.
Anyways, you can go to about:config and set
browser.bookmarks.openInTabClosesMenutofalse- afterwards you can holdCtrl(or just click the middle mouse button) while clicking a bookmark from such popup and the popup should stay open.