I am trying to write a Firefox 3 add-on which will enable me to easily re-tag bookmarks. For example I have some bookmarks tagged \"development\" and some tagged \"Development\"
I can't help much either -- found your question looking for the same kind of answers...
What I have managed to find is the relevant Mozilla documentation. The bookmark system is called Places, and the the database tables are described at https://developer.mozilla.org/en-US/docs/The_Places_database.