Fortunately you can find a solution in the midst of the forum posts. You must download and install an add-on called "bug406646.xpi". The add-on description is the following: "patch for Bug 406646 clicking Bookmarks menu when Firefox starts, tries to add current page as bookmark." I tested this fix and it works like a charm!
Monday, March 2, 2009
I've been struggling with a Firefox bug since version 3.0 came out. It's a misbehavior of the "Bookmarks" and "History" drop-down menus. Sometimes when you click on them the first item in the drop-down list ("Bookmark This Page" and "Back") is called into action and the drop-down menu is not shown. The bug is extremely annoying, particularly because it happens in a random fashion. It has been documented for example in this forum.