Just to add some more details to this: it's worth noting it's not just bookmarks, but all browser history (and associated features, like URLbar auto-completion, or "Top Sites" on new tab page), is also broken.
The specific message shown at startup is: > The bookmarks and history system will not be functional because one of > Firefox's files is in use by another application. Some security software > can cause this problem. ...in a red notification bar at the top of the page. There is a button on the notification that leads to this help page: https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional The two suggestions there (restarting, and creating a new places database) do not work. According to `lsof`, nothing else is accessing places.sqlite, and firefox-esr is able to access the places DB just fine. I am also on Debian 9.5 with firefox 62.0-1 from unstable. Hope that helps! Thank you, -- Felix