Bookmarks view is not working properly

Several days ago all the 'favourite tags' that I'd added to my del.icio.us toolbar (Firefox extension) disappeared from the list of options available to me in 'bookmarks view' and so far I have been unable to re-add them.

These are the steps I'm following to try and re-add them:

- I open the 'Manage Favourite Tags' dialogue.
- When I type in the input field, the drop-down hint list works and I am able to select the tag I need.
- When I click on the 'add tag' button the tag is added to my list of 'favourite tags'
- When I click on the 'OK' button, the dialogue disappears (as expected) but the tags don't appear in the drop-down list for the 'bookmarks view'.
- When I re-open the 'Manage Favourite Tags' dialogue, the tags I just added have disappeared.

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1