This add-on is pretty great but there are time when it completely removes all my data and I have to basically re-start and re-setup all my containers and say which sites open up where for no reason.
Just happened tonight where my three pinned tabs were all of sudden closed (about 20 seconds after just freshly opening the browser) and my custom containers don't exist anymore.
Could be my own issue where I use Firefox Nightly during the day and sync with Firefox Beta in the evenings so the sync-ing process messes things up but I don't know.
Makes me sad.