I've been using containers for some time now (probably since not long after it was announced) to keep my twitter accounts separate, and I've never had to reset or update my preferences.

On at least 3 separate occasions now I've gone to open a container tab, and found that I was back to the default set of (Work, Personal, Shopping, I think). Even better is when this happens, it also resets the count on how many container tabs you've opened, so near the end of the day I'll go to shift containers and get blocked by a "Congrats! You've opened 100 container tabs!" that needs to be dismissed.

This has happened to me several times as well. I use them with the temporary container tabs add-on (so, short-lived containers by default, plus a selection of specific sites that I retain information for, with strict cross-domain isolation), and let me tell you, losing that configuration is painful after setting it up.

The fact that you can't sync container configuration between devices is also a huge pain point, when you have a nontrivial setup.

I still use them, but I accept that I'm going to endure some pain now and then; I can't recommend Firefox containers to people who just want to get work done right now.

Really? Is that a known issue? I haven’t experienced that and I’ve been using containers on Firefox since they were introduced.