Too Quick to Bookmark

All of a sudden (after using Foxmarks/Xmarks for over 2 years) when I click on "Bookmarks" to designate what folder I want to bookmark the site to, the system quickly tells me the site has been bookmarked. I hit "Cancel" and the site does not get bookmarked. Then, I go back and everything works as expected.

This seems to happen only the first time I go to bookmark something in a FireFox session.