Missing folder of bookmarks in Firefox

[LostAngeles]

Everything else is still there, but my sub-folder of knitting bookmarks is gone from Firefox. I've lost all my bookmarks out of Firefox, but never a single folder. Short of my Macbook actually having been tampered with (since I had forgotten to lock my screensaver with my password), I can't think what would have done this.

Someone find me a reason to not raise bloody hell in this room...