I tried Firefox 44 - 64 bit release candidate 2 (Jan 21) and it unfortunately erased my Firefox passwords. I tried going back to Firefox 43 but it did not recover the passwords. I sent Mozilla feedback about this so hopefully the release version will not have this bug. Fortunately I had the Mozilla directory (Appdata/roaming) backed up so after I reverted back to Firefox 43 I was able to recover my passwords. This problem happened on both my laptop and desktop.