The firefox bookmarks work for me (you need to add at least a tag or they will be discarded, you can't add bookmarks first and tag them later).
I find Firefox support is somewhat limited at the moment, anyway:
- You can only add them one at a time, it seems. If I drag a bunch of bookmarks from Firefox's bookmark organizer, only one of them is recognized.
- Firefox tags associated to the bookmark are ignored (on initial add, and when using the "import" option). I know there are feature requests to add some sort of tag syncing. While that would be nice, it's probably not an easy thing to manage. I would be happy if I could just import them.
These are not meant as criticism but suggestions, I find TaggedFrog is great 