It's a long-standing bug that also affects me. It's quite annoying since it's easy to irreversibly hose up your sync account by going over the remote storage quota. Maybe you don't have a Firefox account and/or sync setup?
There are related issues opened for Temporary Containers, MAC and Firefox and at least from the public discussions not much is happening about it.
I use Temporary containers heavily and the MAC sync is also enabled but I never see anything like this. Sometimes 1-2 container it remains but I can delete it manually.
Maybe I'm lucky with this.
Here is the issue if you are interested. It's still not closed:
https://github.com/stoically/temporary-containers/issues/371
> The only thing I miss is Vimperator. Modern alternatives are full of glitches because of inherent limitations in the WebExtensions API.
Didn't use Vimperator, but I found Tridactyl to be pretty good, especially their hinting mode.
Are you setting this option to something else?
Temporary Containers works really well for me. I have per domain isolation, which only breaks very very few sites (Gmail and Outlook 365). For those I have regular persistent containers. Alternatively, I can always open a new private window where I don't have this plugin active.
uBlock Origin + Temporary Containers + ClearURLs are a great setup for privacy and security. Actually, I don't need much else aside from a VPN and a few settings in my user.js.
The only thing I miss is Vimperator. Modern alternatives are full of glitches because of inherent limitations in the WebExtensions API.