Firefox Bookmarks are saved in the table moz_bookmarks in the database file places.sqlite.
see table overview: http://www.forensicswiki.org/wiki/Mozilla_Firefox_3_History_File_Format
a single bookmark may look like this:
id 77 type 1 fk 73 parent 3 position 1 title Google
now I add two Tags to this bookmark in Firefox. Lets name them tag1 and tag2.
The line of the Google bookmark is not changed in the moz_bookmarks table.
Instead the two new tags are added to the end of the table.
example for "tag1":
id 120 type 2 fk (empty) position 0 title tag1
I want to know where Firefox is linking the Google Bookmark to the newly created Tag. There is no reference in the Google Bookmark table entry to tag1 or tag2.
I've looked in every other table of places.sqlite (using SQLite Database Browser, you can get it at SourceForge) and I see nowhere a link between the bookmark and the tags.
Documentation on this subject is very sparse and often 2 years old. The Firefox source code consists of 60.000 files, so it's not easy to do anything with it quickly.